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How to store a procedure or function in a variable (Views: 101)


Problem/Question/Abstract:

Is there some way I can store a procedure or function in a variable so I can call the procedure with the variable? I'm thinking of something similar to where you can declare a variable of a certain object type, then assign different objects of that type to the variable. If it can be done with procedures, how would it be assigned and what would the syntax be to call the procedure?

Answer:

Yes, you can declare a procedural type for functions with the same parameter list and function type. Briefly it looks something like this:


{ ... }
type
  TMathFunc = function(A, B: double): double; {defines signature of function}
  { ... }
var
  mathfunc: TMathFunc;
  answer: double;
  { ... }

{Now if you define two functions}

function Adder(A, B: double): double;
begin
  result := A + B;
end;

function Multiplier(A, B: double): double;
begin
  result := A * B;
end;

begin
  {You can do this}
  mathfunc := Adder;
  answer := mathfunc(5, 9);
  mathfunc := Multiplier;
  answer := mathfunc(5, 9);
end;

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