E2064: Left side cannot be assigned to (Delphi)

This error message is given when you try to modify a read-only object like a constant, a constant parameter, or the return value of function.

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program Produce;

const
  c = 1;

procedure p(const s: string);
begin
  s := 'changed';            (*<-- Error message here*)
end;

function f: PChar;
begin
  f := 'Hello';              (*This is fine - we are setting the return value*)
end;

begin
  c := 2;                    (*<-- Error message here*)
  f := 'h';                  (*<-- Error message here*)
end.

The example assigns to constant parameter, to a constant, and to the result of a function call. All of these are illegal.

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program Solve;

var
  c : Integer = 1;           (*Use an initialized variable*)

procedure p(var s: string);
begin
  s := 'changed';            (*Use variable parameter*)
end;

function f: PChar;
begin
  f := 'Hello';              (*This is fine - we are setting the return value*)
end;

begin
  c := 2;
  f^ := 'h';                 (*This compiles, but will crash at runtime*)
end.

There two ways you can solve this kind of problem: either you change the definition of whatever you are assigning to, so the assignment becomes legal, or you eliminate the assignment.

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