Delphi var parameter setting length comes from the inside of the program

 procedure DoSomeThing(in_cmd: string; var out_strs: array of string);
begin
 ..
 for n := low(out_strs) to high(out_strs) do
 begin< br /> out_strs[n] :='bla bla';
 end;
end;

.
.
.
SetLength(my_out_str, sizer);

DoSomeThing('do it now', my_out_str);
. 
.

type
 TStrDynArray = array of string;

procedure DoSomeThing(in_cmd:string ; var out_strs: TStrDynArray);
begin
 SetLength(out_strs, 2 * Length(inn_cmd));
 ...

procedure DoSomeThing(in_cmd:string; var out_strs: TArray);
begin
 SetLength (out_strs, 2 * Length(inn_cmd));

type
 TDynamicArray = array of string;

procedure Test(var X: array of string);

I am trying to pass some strings to a dynamic string array, in this case it is working:

procedure DoSomeThing(in_cmd: string; var out_strs: array of string);
begin
 ..
 for n := low(out_strs) to high(out_strs) do
 begin
 out_strs[n] :='bla bla';
 end;
end;

Use as in the application:

.
.
.
SetLength(my_out_str, sizer);

DoSomeThing('do it now', my_out_str);
.
. 
But I want to use the SetLength of my_out_str in the program.
Is it possible? 
Yes, it is possible, but you must declare the parameters using the previously defined dynamic array type. You are currently using open array. 
< /p> 
 
type
 TStrDynArray = array of string;

procedure DoSomeThing(in_cmd:string; var out_strs: TStrDynArray);
begin 
 SetLength(out_strs, 2 * Length(inn_cmd));
 ...
Or, use TArray< string>if generics are available (from Delphi 2009) 
procedure DoSomeThing(in_cmd:string; var out_strs: TArray);
begin
 SetLength(out_strs, 2 * Length(inn_cmd));< /pre> 
The reason is that the x array in one context is different from the x array in another context.
 
In the type declaration
 
 
type 
 TDynamicArray = array of string;
It is a dynamic array type and can be resized. Dynamic arrays were introduced in Delphi 4.
In the parameter definition
 < p>
procedure Test(var X: array of string);
 is an open array parameter which means it will accept arrays of different sizes as input. It only needs a pointer ( (I.e. reference) to the first element and the index of the last element in the array. It does not know or care whether the input array is a dynamic array or a static array, so it is not allowed to adjust the length.
Open the array parameter early In Delphi 1.
Further reading
http://rvelthuis.de/articles/articles-openarr.html