On Tue, 1 Dec 2020, Ladislav Karrach via fpc-pascal wrote:
Because MyConst1 is not an *untyped* constant. Only untyped constants
can be used in constant expressions (a pointer to something can be
considered an untyped constant).
The following might work though I did not test it:
=== code begin ===
const
MyStr = 'abc'
MyConst1: AnsiString = MyStr;
MyConst2: TMyRec = (l: Length(MyStr); a: @MyConst1[1]);
=== code end ===
Yes it works, but I must define 2 constants (MyStr and MyConst1), which
is not so nice ;-)
It would be nice to have support for true constants:
const
MyConst1 = 'abc' ;
MyConst2: TMyRec = (l: Length(MyConst1); a: @MyConst1[1]);
But may be that there are technical reasons why it is problematic (may
be that true constants are stored in another memory locations, which can
not be easy addressed)
From a pure language point of view, true constants do not "exist".
They are substituted wherever the compiler finds a reference.
So there is no address in memory.
A typed constant is like a variable (it is the precursor of the initialized
variable), it has an address in memory.
Michael.
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