Function calls are part of expressions (although, using extended syntax, they can be statements too). They are constructed as follows:
Function calls
The variable reference must be a procedural type variable referce. A method designator can only be used in side the method of an object. A qualified method designator can be used outside object methods too.
The function that will get called is the function with a declared parameter list that matches the actual parameter list. This means that
If no matching function is found, then the compiler will generate an error. Depending on the fact of the function is overloaded (i.e. multiple functions with the same name, but different parameter lists) the error will be different.
There are cases when the compiler will not execute the function call in an
expression. This is the case when you are assigning a value to a procedural
type variable, as in the following example:
In the above listing, the assigment to F will not cause the function AddOne
to be called. The assignment to N, however, will call AddOne.
A problem with this syntax is the following construction:
Should the compiler compare the addresses of F and AddOne,
or should it call both functions, and compare the result ? Free Pascal solves this
by deciding that a procedural variable is equivalent to a pointer. Thus the
compiler will give a type mismatch error, since AddOne is considered a
call to a function with integer result, and F is a pointer, Hence a type
mismatch occurs.
How then, should one compare whether F points to the function
AddOne ? To do this, one should use the address operator @:
The left hand side of the boolean expression is an address. The right hand
side also, and so the compiler compares 2 addresses.
How to compare the values that both functions return ? By adding an empty
parameter list:
Remark that this behaviour is not compatible with Delphi syntax.
