Often the D language shares the semantic of C language. This D program compiles with no errors or warnings:


struct Foo { int a, b; }
void main() {
    Foo f;
    if (&f.a < &f.b) {} // first comparison
    int a, b;
    if (&a < &b) {} // second comparison
}


The first comparison is correct, the addresses of a and b are guaranteed to be in order by the C standard, see §6.5.8:5  (ISO/IEC JTC 1, SC 22, WG 14. ISO/IEC 9899:201x: Programming languages—C. Technical Report n1570, Intl. Organization for Standardization, August 2011).

The second comparison is undefined in C according to the C standard §6.5.8:5. Because semantics is given to relational pointer comparisons only where the two addresses share a common base.

I think a compiler is free to reorder the position of the variables a and b on the stack.

So on that D program I suggest the D compiler to give error similar to:

Line 6: Error: cannot apply '<' to different base objects.

See:
http://c-semantics.googlecode.com/files/2012-C-Semantics-Ellison-Rosu-POPL.pdf