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Small Delphi tricks: initialise out parameters in the caller when they are stored in local variables; a Run for TProc

Posted by jpluimers on 2020/12/29

Two small Delphi tricks:

On out parameters

When you have out parameters, and the caller passes local variables for them, remember that:

  1. the compiler then will not issue an “unitialised variable” warning any more because it expects the callee to fill that parameter
  2. if the local variable is non-managed, it will have a random value depending on the call stack state

A RunProc method that executes a TProc

Every so often you want to refactor a method to use two or more different algorithm implementations.

A good start is to have some conditional, to choose the algorithm, then have anonymous methods implement each algorithm.

This quickly gives you a feel of where the local vars of the original method need to go:

  • local to an implementation
  • local to the original method
  • parameters to the algorithm

A parameterless runner can be a good start to call these methods:

procedure RunProc(const AProc: TProc);

You can extend this to TProc<T> and further generic forms, by adding parameters. In that case however, the need to be inside a record (because global methods cannot be generic).


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