FunctionPointerCast¶

Views a procedure through a different signature.

Declaration¶

Syntax¶

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

Arguments¶

Argument	Описание
`arg`	the procedure being viewed.
`to`	the Function whose signature this view has. It is an `Interface`; its body, if any, is not what is called through the cast.
`type`	the type of the result: the FunctionType of `to`.
`value`	the compile time value of the expression, when the frontend could fold it; `nil` otherwise.

Return values¶

The procedure, typed as to.

Описание¶

Nothing is converted. The procedure’s address is unchanged; only the signature the call site uses 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 one situation. Under --implicit-interface, a procedure declared external with no interface (see deftype) gets its signature from the actual arguments at each reference. When two references in the same scope disagree, one inferred Interface cannot serve both. The first-inferred signature stays the canonical procedure under the user-visible name; each later reference that disagrees gets its own Interface symbol, and reaches the procedure through a FunctionPointerCast to it. The call is then a call of a procedure pointer associated with the cast, so the call agrees with its callee, which is the invariant every call in ASR has to satisfy.

Such a program is not standard-conforming: F2018 15.5.2.5 requires the actual arguments at every reference to agree with the dummies of the definition, so two references that disagree with each other cannot both agree with it. gfortran accepts it with -fallow-argument-mismatch. This node is the model LFortran uses for it, and is the model separate compilation gives anyway when the definition is not in this translation unit.

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 with a known interface needs no cast at all.