[AST] how to check if a type is template specification type and get the template paramter?

Clang Frontend
1

Hi, all.

I want to check if a given clang::Type is a std::vector and get the type of xxx.

I tried this if (const auto *tst = llvm::dyn_cast<clang::TemplateSpecializationType>(type)) {} but the condition is always false, it seems that TemplateSpecializationType is not what I think it is.

So can what I want be done?

2

Hi, all.

I want to check if a given `clang::Type` is a std::vector<xxx> and get the type of xxx.

I tried this `if (const auto *tst = llvm::dyn_cast<clang::TemplateSpecializationType>(type)) {}` but the condition is always false, it seems that TemplateSpecializationType is not what I think it is.

So can what I want be done?

Assuming the template specialization type is not dependent (so you have a TemplateSpecializationType
and not a DependentTemplateSpecializationType), use Type::getAs<TemplateSpecializationType> to
look through sugar. Consider:

namespace N {
  template <typename T> struct S {};
}

using type = N::S<int>;

The AST for the type alias declaration is:

-TypeAliasDecl 0x559082acee80 <line:5:1, col:22> col:7 type 'N::S<int>':'N::S<int>'
  `-ElaboratedType 0x559082acedc0 'N::S<int>' sugar <-------------------
    `-TemplateSpecializationType 0x559082aced70 'S<int>' sugar S
      >-TemplateArgument type 'int'
      > `-BuiltinType 0x559082a882e0 'int'
      `-RecordType 0x559082aced40 'N::S<int>'
        `-ClassTemplateSpecialization 0x559082acec40 'S'

3

Hi Bruno, it works, are there suggestions saying that always using Type::getAs<> rather than llvm::dyn_cast<>?

4

Hi Bruno, it works, are there suggestions saying that always using Type::getAs<> rather than llvm::dyn_cast<>?

Yes, generally you should use T->getAs<…> instead of dyn_cast<…>(T) if you want to inspect the semantics of the type rather than the outermost level of type sugar. See also http://clang.llvm.org/docs/InternalsManual.html#canonical-types