FunctionPointerCast¶

Views a procedure through a different procedure type.

Declaration¶

Syntax¶

FunctionPointerCast(expr arg, symbol? to, ttype type, expr? value)

Arguments¶

Argument	Description
`arg`	the procedure being viewed: a procedure, a dummy procedure or a procedure pointer.
`to`	the Function whose signature this view has. It is an explicit interface; its body, if any, is not what is called through the cast. `nil` for a cast to the opaque procedure type.
`type`	the type of the result: the FunctionType of `to`, or, without `to`, the opaque procedure type (deftype `ImplicitInterface`, see deftype).
`value`	the compile time value of the expression, when the frontend could fold it; `nil` otherwise.

Return values¶

The procedure, typed as type.

Description¶

Nothing is converted. The procedure’s address is unchanged; only the signature used to reach it differs. It is the procedure-valued counterpart of BitCast, and the same warning applies: whether the call is correct is not decided here.

It exists for procedures with an implicit interface (see deftype), whose type says nothing about their arguments:

Calls. Each reference to a procedure with an implicit interface builds an Interface from its own actual arguments (and result type), filed in the calling procedure as name~fpcast and shared by references with the same signature. The procedure is associated with a procedure-pointer temporary through a FunctionPointerCast to that interface right before the statement (before each evaluation of a DO WHILE condition), and the call is a call of that temporary, so the call agrees with its callee. The temporary belongs to the scope of the statements it is associated in (e.g. a statement function has its own). A procedure with an implicit interface is not a specification function, so it is never referenced in a specification expression.
Procedure actuals and pointer targets. A procedure passed to a dummy procedure, or associated with a procedure pointer, whose type differs from its own is cast to the type of the dummy or pointer: to the opaque type, without to, for a dummy with an implicit interface, and to the dummy’s interface (or a copy of it in the caller) for a procedure with an implicit interface passed to a dummy with an explicit one.

A cast to a type other than the opaque one needs to: the interface carries the argument declarations (derived types, character and array physical types) the lowering of the signature depends on.

Two references with different argument lists are not standard-conforming (F2018 15.5.2.5 requires the actual arguments at every reference to agree with the dummies of the definition). gfortran accepts such a program with -fallow-argument-mismatch; this node is the model LFortran uses for it, and the model separate compilation gives anyway.

Do not produce this node for anything else. A conversion between data types is Cast; reinterpreting the bits of a value is BitCast; a procedure passed where its own explicit interface is expected needs no cast.