Closed
Description
The following code is an example for aggregate deduction guides.
template <typename T1, typename T2>
struct Foo {
T1 t1;
T2 t2;
};
template<typename X, typename Y>
using A = Foo<X, Y>;
A a = {1, 2};
The related AST DeductionGuideDecl nodes look like:
|-FunctionTemplateDecl 0x5633ce70b420 <line:7:1, line:8:19> col:1 implicit <deduction guide for A>
| |-TemplateTypeParmDecl 0x5633ce70ad90 <line:7:10, col:19> col:19 typename depth 0 index 0 X
| |-TemplateTypeParmDecl 0x5633ce70ae18 <col:22, col:31> col:31 typename depth 0 index 1 Y
| `-CXXDeductionGuideDecl 0x5633ce70b360 <col:1, line:8:19> col:1 implicit <deduction guide for A> 'auto () -> Foo<type-parameter-0-0, type-parameter-0-1>'
|-FunctionTemplateDecl 0x5633ce70c458 <line:7:1, line:8:19> col:1 implicit <deduction guide for A>
| |-TemplateTypeParmDecl 0x5633ce70b480 <line:7:10, col:19> col:19 typename depth 0 index 0 X
| |-TemplateTypeParmDecl 0x5633ce70b508 <col:22, col:31> col:31 typename depth 0 index 1 Y
| `-CXXDeductionGuideDecl 0x5633ce70c390 <col:1, line:8:19> col:1 implicit <deduction guide for A> 'auto (Foo<type-parameter-0-0, type-parameter-0-1>) -> Foo<type-parameter-0-0, type-parameter-0-1>'
| `-ParmVarDecl 0x5633ce70b8e8 <line:2:8> col:8 'Foo<type-parameter-0-0, type-parameter-0-1>'
`-FunctionTemplateDecl 0x5633ce70c748 <line:1:1, line:2:8> col:8 implicit <deduction guide for Foo>
|-TemplateTypeParmDecl 0x5633ce6eac18 <line:1:11, col:20> col:20 referenced typename depth 0 index 0 T1
|-TemplateTypeParmDecl 0x5633ce6eacd8 <col:24, col:33> col:33 referenced typename depth 0 index 1 T2
|-CXXDeductionGuideDecl 0x5633ce70c678 <line:2:8> col:8 implicit <deduction guide for Foo> 'auto (T1, T2) -> Foo<T1, T2>'
| |-ParmVarDecl 0x5633ce70c588 <col:8> col:8 'T1'
| `-ParmVarDecl 0x5633ce70c608 <col:8> col:8 'T2'
`-CXXDeductionGuideDecl 0x5633ce70ce68 <col:8> col:8 implicit used <deduction guide for Foo> 'auto (int, int) -> Foo<int, int>' implicit_instantiation
|-TemplateArgument type 'int'
| `-BuiltinType 0x5633ce699230 'int'
|-TemplateArgument type 'int'
| `-BuiltinType 0x5633ce699230 'int'
|-ParmVarDecl 0x5633ce70cad8 <col:8> col:8 'int'
`-ParmVarDecl 0x5633ce70cb88 <col:8> col:8 'int'
We have issues:
- we don't have the aggregate deduction guide decl for the alias
A, we should synthesize one from the Foo'sauto (T1, T2) -> Foo<T1, T2>; - the template argument deduction is performed on deduction guide for
Foo, which should be performed on use this synthesized guide decl (the instantiation should not be performed on deduction guide forA);