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Cannot use a typedesc variable in a template #9611

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bluenote10 opened this issue Nov 3, 2018 · 1 comment

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commented Nov 3, 2018

Passing a typedesc to a template seems to fail when the parameter is a typedesc variable:

Example

proc aProc(A: typedesc) =
  var a: A

template aTemplate(A: typedesc) = 
  var a: A

var T: typedesc[int]
aProc(int)       # works with concrete type
aTemplate(int)   # works with concrete type
aProc(T)         # works with typedesc variable
aTemplate(T)     # fails with typedesc variable

Current Output

test.nim(11, 11) Error: type expected

Interestingly passing the typedesc variable to the template works, if the template does not use the type explicitly in variable/type/function definitions and only calls procs that take typedescs. For instance the code compiles when changing the typedesc to

template aTemplate(A: typedesc) = 
  aProc(A)

The common work-around of using a local type alias like type AA = A doesn't seem to help here.

@Araq

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commented Nov 3, 2018

var T: typedesc[int] is not valid Nim and should be rejected.

@dom96 dom96 added the Error messages label Nov 3, 2018

@Araq Araq closed this in ae27f8a Nov 3, 2018

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