传递多态参数时，泛型没有特定功能

Question

I have created an interface for the following functions

Interface numd
  Module Procedure :: numcl_int8,    numcl_int16  
  Module Procedure :: numcl_int32,   numcl_int64  
  Module Procedure :: numcl_real32,  numcl_real64  
  Module Procedure :: numcl_real128  
End Interface numd

The functions as defined as follows for output as Int8, Int16, Int32, Int64, Real32, Real64, Real128.

Function numcl_int8 (t, mold) Result (b)
  Integer (Int8) :: b
  Class (*), Intent (In) :: t
  Integer (Int8), Intent (InOut) :: mold
End Function numcl_int8

I am getting error

There is no specific function for the generic 'numd' at (1) 

when calling numd in the following subroutine

Subroutine opscanc (ct)
  Class (*), Intent (Out) :: ct
  ct = numd (5, mold=ct)
End Subroutine opscanc

How can I solve this problem?

Answer 1

The second actual argument ( mold=ct ) in the call to numd in the opscanc subroutine has a declared type that is unlimited polymorphic. Based on your example of the interface of the specific procedures, none of the specific procedures in the generic interface have the type of the second dummy argument as unlimited polymorphic.

An unlimited polymorphic actual argument is not type compatible with a dummy argument that has some declared type, so there is no matching specific procedure to call.

(The direction of the comparison is important here - an actual argument that has some declared type is compatible with a dummy argument that is unlimited polymorphic - hence the default integer literal constant 5 can be associated with the first dummy argument that is unlimited polymorphic.)

You either need to provide such a matching specific procedure, or use a SELECT TYPE construct inside opscanc to access the object nominated by ct via a declared type that is its dynamic type (or a parent type of its dynamic type).