for-in loop

What is translated > Statements > for loop's > for-in loop

A Delphi 'for-in' loop has the following general form:

var

  A: TypeName;

begin

  for A in B do

    DoSomething(A);

end;

Depending on the type of 'B', the variable 'A' can represent:

Strings, arrays, and sets are usually translated into C++11 range-based 'for' loops:

TypeName A;

for (TypeName element_0 : B)

{

    A = element_0;

    DoSomething(A);

}

The additional variable 'element_0' allows Delphi2Cpp to preserve the declaration and assignment semantics of the original Delphi loop variable.

Open Arrays

For C++Builder open-array parameters, the array is passed as a pointer together with its highest valid index. A cast may therefore be required before the value can be used in a range-based 'for' loop:

template<typename T>

void __fastcall ArrayOfConstLoop(const T* B, int B_maxidx)

{

    T A;

    for (auto element_0 : *(T (*)[B_maxidx + 1])B)

    {

        A = element_0;

        DoSomething(A);

    }

}

'B_maxidx' is the highest valid index, not the number of elements. The corresponding array size is therefore 'B_maxidx + 1'.

The iterator support required for sets and open arrays is defined in 'd2c_systypes.h'.

Enumerator Types

A container can support Delphi 'for-in' loops by providing a 'GetEnumerator()' method. The enumerator is obtained once and then used for the entire loop:

auto enumerator_0 = B->GetEnumerator();

while (enumerator_0->MoveNext())

{

    TypeName A = enumerator_0->Current;

    DoSomething(A);

}

Calling 'GetEnumerator()' only once is important because each call may create or return a different enumerator instance.

This page belongs to the Delphi2Cpp Documentation