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/** Helpers for working with user-defined attributes that can be attached to function or method to modify its behavior. In some sense those are similar to Python decorator. D does not support this feature natively but it can be emulated within certain code generation framework. Copyright: © 2013 RejectedSoftware e.K. License: Subject to the terms of the MIT license, as written in the included LICENSE.txt file. Authors: Михаил Страшун */ module vibe.internal.meta.funcattr; import std.traits : isInstanceOf, ReturnType; import vibe.internal.meta.traits : RecursiveFunctionAttributes; /// example unittest { struct Context { int increment; string token; bool updated = false; } static int genID(Context* context) { static int id = 0; return (id += context.increment); } static string update(string result, Context* context) { context.updated = true; return result ~ context.token; } class API { @before!genID("id") @after!update() string handler(int id, string name, string text) { import std.string : format; return format("[%s] %s : %s", id, name, text); } } auto api = new API(); auto context = new Context(5, " | token"); auto funcattr = createAttributedFunction!(API.handler)(context); auto result = funcattr(&api.handler, "Developer", "Hello, World!"); assert (result == "[5] Developer : Hello, World! | token"); assert (context.updated); } /** Marks function/method for usage with `AttributedFunction`. Former will call a Hook before calling attributed function/method and provide its return value as input parameter. Params: Hook = function/method symbol to run before attributed function/method parameter_name = name in attributed function/method parameter list to bind result to Returns: internal attribute struct that embeds supplied information */ auto before(alias Hook)(string parameter_name) { return InputAttribute!Hook(parameter_name); } /// unittest { int genID() { return 42; } @before!genID("id") void foo(int id, double something) {} } /** Marks function/method for usage with `AttributedFunction`. Former will call a Hook after calling attributed function/method and provide its return value as a single input parameter for a Hook. There can be only one "after"-attribute attached to a single symbol. Params: Hook = function/method symbol to run after attributed function/method Returns: internal attribute struct that embeds supplied information */ @property auto after(alias Function)() { return OutputAttribute!Function(); } /// unittest { auto filter(int result) { return result; } @after!filter() int foo() { return 42; } } /** Checks if parameter is calculated by one of attached functions. Params: Function = function symbol to query for attributes name = parameter name to check Returns: `true` if it is calculated */ template IsAttributedParameter(alias Function, string name) { import std.traits : FunctionTypeOf; static assert (is(FunctionTypeOf!Function)); private { alias Data = AttributedParameterMetadata!Function; template Impl(T...) { static if (T.length == 0) { enum Impl = false; } else { static if (T[0].name == name) { enum Impl = true; } else { enum Impl = Impl!(T[1..$]); } } } } enum IsAttributedParameter = Impl!Data; } template HasFuncAttributes(alias Func) { import std.typetuple; enum HasFuncAttributes = (anySatisfy!(isOutputAttribute, __traits(getAttributes, Func)) || anySatisfy!(isInputAttribute, __traits(getAttributes, Func))); } unittest { string foo() { return "Hello"; } string bar(int) { return foo(); } @before!foo("b") void baz1(string b) {} @after!bar() string baz2() { return "Hi"; } @before!foo("b") @after!bar() string baz3(string b) { return "Hi"; } static assert (HasFuncAttributes!baz1); static assert (HasFuncAttributes!baz2); static assert (HasFuncAttributes!baz3); string foobar1(string b) { return b; } @("Irrelevant", 42) string foobar2(string b) { return b; } static assert (!HasFuncAttributes!foobar1); static assert (!HasFuncAttributes!foobar2); } /** Computes the given attributed parameter using the corresponding @before modifier. */ auto computeAttributedParameter(alias FUNCTION, string NAME, ARGS...)(ARGS args) { import std.typetuple : Filter; static assert(IsAttributedParameter!(FUNCTION, NAME), "Missing @before attribute for parameter "~NAME); alias input_attributes = Filter!(isInputAttribute, RecursiveFunctionAttributes!FUNCTION); foreach (att; input_attributes) static if (att.parameter == NAME) { return att.evaluator(args); } assert(false); } /** Computes the given attributed parameter using the corresponding @before modifier. This overload tries to invoke the given function as a member of the $(D ctx) parameter. It also supports accessing private member functions using the $(D PrivateAccessProxy) mixin. */ auto computeAttributedParameterCtx(alias FUNCTION, string NAME, T, ARGS...)(T ctx, ARGS args) { static if (__VERSION__ >= 2072) import std.typetuple : AliasSeq, Filter; else import std.typetuple : AliasSeq = TypeTuple, Filter; static assert(IsAttributedParameter!(FUNCTION, NAME), "Missing @before attribute for parameter "~NAME); alias input_attributes = Filter!(isInputAttribute, RecursiveFunctionAttributes!FUNCTION); foreach (att; input_attributes) static if (att.parameter == NAME) { static if (!__traits(isStaticFunction, att.evaluator)) { static if (is(typeof(ctx.invokeProxy__!(att.evaluator)(args)))) return ctx.invokeProxy__!(att.evaluator)(args); else return __traits(getMember, ctx, __traits(identifier, att.evaluator))(args); } else { return att.evaluator(args); } } assert(false); } /** Helper mixin to support private member functions for $(D @before) attributes. */ mixin template PrivateAccessProxy() { auto invokeProxy__(alias MEMBER, ARGS...)(ARGS args) { return MEMBER(args); } } /// unittest { class MyClass { @before!computeParam("param") void method(bool param) { assert(param == true); } private bool computeParam() { return true; } } } /** Processes the function return value using all @after modifiers. */ ReturnType!FUNCTION evaluateOutputModifiers(alias FUNCTION, ARGS...)(ReturnType!FUNCTION result, ARGS args) { import std.string : format; import std.traits : ParameterTypeTuple, ReturnType, fullyQualifiedName; import std.typetuple : Filter; import vibe.internal.meta.typetuple : Compare, Group; alias output_attributes = Filter!(isOutputAttribute, RecursiveFunctionAttributes!FUNCTION); foreach (OA; output_attributes) { import std.typetuple : TypeTuple; static assert ( Compare!( Group!(ParameterTypeTuple!(OA.modificator)), Group!(ReturnType!FUNCTION, ARGS) ), format( "Output attribute function '%s%s' argument list " ~ "does not match provided argument list %s", fullyQualifiedName!(OA.modificator), ParameterTypeTuple!(OA.modificator).stringof, TypeTuple!(ReturnType!FUNCTION, ARGS).stringof ) ); result = OA.modificator(result, args); } return result; } /// unittest { int foo() { return 42; } @before!foo("name1") void bar(int name1, double name2) { } static assert (IsAttributedParameter!(bar, "name1")); static assert (!IsAttributedParameter!(bar, "name2")); static assert (!IsAttributedParameter!(bar, "oops")); } // internal attribute definitions private { struct InputAttribute(alias Function) { alias evaluator = Function; string parameter; } struct OutputAttribute(alias Function) { alias modificator = Function; } template isInputAttribute(T...) { enum isInputAttribute = (T.length == 1) && isInstanceOf!(InputAttribute, typeof(T[0])); } unittest { void foo() {} enum correct = InputAttribute!foo("name"); enum wrong = OutputAttribute!foo(); static assert (isInputAttribute!correct); static assert (!isInputAttribute!wrong); } template isOutputAttribute(T...) { enum isOutputAttribute = (T.length == 1) && isInstanceOf!(OutputAttribute, typeof(T[0])); } unittest { void foo() {} enum correct = OutputAttribute!foo(); enum wrong = InputAttribute!foo("name"); static assert (isOutputAttribute!correct); static assert (!isOutputAttribute!wrong); } } // tools to operate on InputAttribute tuple private { // stores metadata for single InputAttribute "effect" struct Parameter { // evaluated parameter name string name; // that parameter index in attributed function parameter list int index; // fully qualified return type of attached function string type; // for non-basic types - module to import string origin; } /** Used to accumulate various parameter-related metadata in one tuple in one go. Params: Function = attributed functon / method symbol Returns: TypeTuple of Parameter instances, one for every Function parameter that will be evaluated from attributes. */ template AttributedParameterMetadata(alias Function) { import std.array : join; import std.typetuple : Filter, staticMap, staticIndexOf; import std.traits : ParameterIdentifierTuple, ReturnType, fullyQualifiedName, moduleName; private alias attributes = Filter!( isInputAttribute, RecursiveFunctionAttributes!Function ); private alias parameter_names = ParameterIdentifierTuple!Function; /* Creates single Parameter instance. Used in pair with staticMap. */ template BuildParameter(alias attribute) { enum name = attribute.parameter; static assert ( is (ReturnType!(attribute.evaluator)) && !(is(ReturnType!(attribute.evaluator) == void)), "hook functions attached for usage with `AttributedFunction` " ~ "must have a return type" ); static if (is(typeof(moduleName!(ReturnType!(attribute.evaluator))))) { enum origin = moduleName!(ReturnType!(attribute.evaluator)); } else { enum origin = ""; } enum BuildParameter = Parameter( name, staticIndexOf!(name, parameter_names), fullyQualifiedName!(ReturnType!(attribute.evaluator)), origin ); import std.string : format; static assert ( BuildParameter.index >= 0, format( "You are trying to attach function result to parameter '%s' " ~ "but there is no such parameter for '%s(%s)'", name, fullyQualifiedName!Function, join([ parameter_names ], ", ") ) ); } alias AttributedParameterMetadata = staticMap!(BuildParameter, attributes); } // no false attribute detection unittest { @(42) void foo() {} static assert (AttributedParameterMetadata!foo.length == 0); } // does not compile for wrong attribute data unittest { int attached1() { return int.init; } void attached2() {} @before!attached1("doesnotexist") void bar(int param) {} @before!attached2("param") void baz(int param) {} // wrong name static assert (!__traits(compiles, AttributedParameterMetadata!bar)); // no return type static assert (!__traits(compiles, AttributedParameterMetadata!baz)); } // generates expected tuple for valid input unittest { int attached1() { return int.init; } double attached2() { return double.init; } @before!attached1("two") @before!attached2("three") void foo(string one, int two, double three) {} alias result = AttributedParameterMetadata!foo; static assert (result.length == 2); static assert (result[0] == Parameter("two", 1, "int")); static assert (result[1] == Parameter("three", 2, "double")); } /** Combines types from arguments of initial `AttributedFunction` call with parameters (types) injected by attributes for that call. Used to verify that resulting argument list can be passed to underlying attributed function. Params: ParameterMeta = Group of Parameter instances for extra data to add into argument list ParameterList = Group of types from initial argument list Returns: type tuple of expected combined function argument list */ template MergeParameterTypes(alias ParameterMeta, alias ParameterList) { import vibe.internal.meta.typetuple : isGroup, Group; static assert (isGroup!ParameterMeta); static assert (isGroup!ParameterList); static if (ParameterMeta.expand.length) { enum Parameter meta = ParameterMeta.expand[0]; static assert (meta.index <= ParameterList.expand.length); static if (meta.origin != "") { mixin("static import " ~ meta.origin ~ ";"); } mixin("alias type = " ~ meta.type ~ ";"); alias PartialResult = Group!( ParameterList.expand[0..meta.index], type, ParameterList.expand[meta.index..$] ); alias MergeParameterTypes = MergeParameterTypes!( Group!(ParameterMeta.expand[1..$]), PartialResult ); } else { alias MergeParameterTypes = ParameterList.expand; } } // normal unittest { import vibe.internal.meta.typetuple : Group, Compare; alias meta = Group!( Parameter("one", 2, "int"), Parameter("two", 3, "string") ); alias initial = Group!( double, double, double ); alias merged = Group!(MergeParameterTypes!(meta, initial)); static assert ( Compare!(merged, Group!(double, double, int, string, double)) ); } // edge unittest { import vibe.internal.meta.typetuple : Group, Compare; alias meta = Group!( Parameter("one", 3, "int"), Parameter("two", 4, "string") ); alias initial = Group!( double, double, double ); alias merged = Group!(MergeParameterTypes!(meta, initial)); static assert ( Compare!(merged, Group!(double, double, double, int, string)) ); } // out-of-index unittest { import vibe.internal.meta.typetuple : Group; alias meta = Group!( Parameter("one", 20, "int"), ); alias initial = Group!( double ); static assert ( !__traits(compiles, MergeParameterTypes!(meta, initial)) ); } } /** Entry point for `funcattr` API. Helper struct that takes care of calling given Function in a such way that part of its arguments are evalutated by attached input attributes (see `before`) and output gets post-processed by output attribute (see `after`). One such structure embeds single attributed function to call and specific argument type list that can be passed to attached functions. Params: Function = attributed function StoredArgTypes = Group of argument types for attached functions */ struct AttributedFunction(alias Function, alias StoredArgTypes) { import std.traits : isSomeFunction, ReturnType, FunctionTypeOf, ParameterTypeTuple, ParameterIdentifierTuple; import vibe.internal.meta.typetuple : Group, isGroup, Compare; import std.functional : toDelegate; import std.typetuple : Filter; static assert (isGroup!StoredArgTypes); static assert (is(FunctionTypeOf!Function)); /** Stores argument tuple for attached function calls Params: args = tuple of actual argument values */ void storeArgs(StoredArgTypes.expand args) { m_storedArgs = args; } /** Used to invoke configured function/method with all attached attribute functions. As aliased method symbols can't be called without the context, explicit providing of delegate to call is required Params: dg = delegated created from function / method to call args = list of arguments to dg not provided by attached attribute function Return: proxies return value of dg */ ReturnType!Function opCall(T...)(FunctionDg dg, T args) { import std.traits : fullyQualifiedName; import std.string : format; enum hasReturnType = is(ReturnType!Function) && !is(ReturnType!Function == void); static if (hasReturnType) { ReturnType!Function result; } // check that all attached functions have conforming argument lists foreach (uda; input_attributes) { static assert ( Compare!( Group!(ParameterTypeTuple!(uda.evaluator)), StoredArgTypes ), format( "Input attribute function '%s%s' argument list " ~ "does not match provided argument list %s", fullyQualifiedName!(uda.evaluator), ParameterTypeTuple!(uda.evaluator).stringof, StoredArgTypes.expand.stringof ) ); } static if (hasReturnType) { result = prepareInputAndCall(dg, args); } else { prepareInputAndCall(dg, args); } static assert ( output_attributes.length <= 1, "Only one output attribute (@after) is currently allowed" ); static if (output_attributes.length) { import std.typetuple : TypeTuple; static assert ( Compare!( Group!(ParameterTypeTuple!(output_attributes[0].modificator)), Group!(ReturnType!Function, StoredArgTypes.expand) ), format( "Output attribute function '%s%s' argument list " ~ "does not match provided argument list %s", fullyQualifiedName!(output_attributes[0].modificator), ParameterTypeTuple!(output_attributes[0].modificator).stringof, TypeTuple!(ReturnType!Function, StoredArgTypes.expand).stringof ) ); static if (hasReturnType) { result = output_attributes[0].modificator(result, m_storedArgs); } else { output_attributes[0].modificator(m_storedArgs); } } static if (hasReturnType) { return result; } } /** Convenience wrapper tha creates stub delegate for free functions. As those do not require context, passing delegate explicitly is not required. */ ReturnType!Function opCall(T...)(T args) if (!is(T[0] == delegate)) { return this.opCall(toDelegate(&Function), args); } private { // used as an argument tuple when function attached // to InputAttribute is called StoredArgTypes.expand m_storedArgs; // used as input type for actual function pointer so // that both free functions and methods can be supplied alias FunctionDg = typeof(toDelegate(&Function)); // information about attributed function arguments alias ParameterTypes = ParameterTypeTuple!Function; alias parameter_names = ParameterIdentifierTuple!Function; // filtered UDA lists alias input_attributes = Filter!(isInputAttribute, __traits(getAttributes, Function)); alias output_attributes = Filter!(isOutputAttribute, __traits(getAttributes, Function)); } private { /** Does all the magic necessary to prepare argument list for attributed function based on `input_attributes` and `opCall` argument list. Catches all name / type / size mismatch erros in that domain via static asserts. Params: dg = delegate for attributed function / method args = argument list from `opCall` Returns: proxies return value of dg */ ReturnType!Function prepareInputAndCall(T...)(FunctionDg dg, T args) if (!Compare!(Group!T, Group!(ParameterTypeTuple!Function))) { alias attributed_parameters = AttributedParameterMetadata!Function; // calculated combined input type list alias Input = MergeParameterTypes!( Group!attributed_parameters, Group!T ); import std.traits : fullyQualifiedName; import std.string : format; static assert ( Compare!(Group!Input, Group!ParameterTypes), format( "Calculated input parameter type tuple %s does not match " ~ "%s%s", Input.stringof, fullyQualifiedName!Function, ParameterTypes.stringof ) ); // this value tuple will be used to assemble argument list Input input; foreach (i, uda; input_attributes) { // each iteration cycle is responsible for initialising `input` // tuple from previous spot to current attributed parameter index // (including) enum index = attributed_parameters[i].index; static if (i == 0) { enum lStart = 0; enum lEnd = index; enum rStart = 0; enum rEnd = index; } else { enum previousIndex = attributed_parameters[i - 1].index; enum lStart = previousIndex + 1; enum lEnd = index; enum rStart = previousIndex + 1 - i; enum rEnd = index - i; } static if (lStart != lEnd) { input[lStart..lEnd] = args[rStart..rEnd]; } // during last iteration cycle remaining tail is initialised // too (if any) static if ((i == input_attributes.length - 1) && (index != input.length - 1)) { input[(index + 1)..$] = args[(index - i)..$]; } input[index] = uda.evaluator(m_storedArgs); } // handle degraded case with no attributes separately static if (!input_attributes.length) { input[] = args[]; } return dg(input); } /** `prepareInputAndCall` overload that operates on argument tuple that exactly matches attributed function argument list and thus gets updated by attached function instead of being merged with it */ ReturnType!Function prepareInputAndCall(T...)(FunctionDg dg, T args) if (Compare!(Group!T, Group!(ParameterTypeTuple!Function))) { alias attributed_parameters = AttributedParameterMetadata!Function; foreach (i, uda; input_attributes) { enum index = attributed_parameters[i].index; args[index] = uda.evaluator(m_storedArgs); } return dg(args); } } } /// example unittest { import std.conv; static string evaluator(string left, string right) { return left ~ right; } // all attribute function must accept same stored parameters static int modificator(int result, string unused1, string unused2) { return result * 2; } @before!evaluator("a") @before!evaluator("c") @after!modificator() static int sum(string a, int b, string c, double d) { return to!int(a) + to!int(b) + to!int(c) + to!int(d); } // ("10", "20") - stored arguments for evaluator() auto funcattr = createAttributedFunction!sum("10", "20"); // `b` and `d` are unattributed, thus `42` and `13.5` will be // used as their values int result = funcattr(42, 13.5); assert(result == (1020 + 42 + 1020 + to!int(13.5)) * 2); } // testing other prepareInputAndCall overload unittest { import std.conv; static string evaluator(string left, string right) { return left ~ right; } // all attribute function must accept same stored parameters static int modificator(int result, string unused1, string unused2) { return result * 2; } @before!evaluator("a") @before!evaluator("c") @after!modificator() static int sum(string a, int b, string c, double d) { return to!int(a) + to!int(b) + to!int(c) + to!int(d); } auto funcattr = createAttributedFunction!sum("10", "20"); // `a` and `c` are expected to be simply overwritten int result = funcattr("1000", 42, "1000", 13.5); assert(result == (1020 + 42 + 1020 + to!int(13.5)) * 2); } /** Syntax sugar in top of AttributedFunction Creates AttributedFunction with stored argument types that match `T` and stores `args` there before returning. */ auto createAttributedFunction(alias Function, T...)(T args) { import vibe.internal.meta.typetuple : Group; AttributedFunction!(Function, Group!T) result; result.storeArgs(args); return result; } /// unittest { void foo() {} auto funcattr = createAttributedFunction!foo(1, "2", 3.0); import std.typecons : tuple; assert (tuple(funcattr.m_storedArgs) == tuple(1, "2", 3.0)); }