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That's because of the implementation details of C#. If I make a const pointer in C, it's obviously not a compile-time value, because the memory location can't b

by kedean 10y ago

That's because of the implementation details of C#. If I make a const pointer in C, it's obviously not a compile-time value, because the memory location can't be guaranteed at compile time. Const values in C are definitely able to be assigned from variables. Very few languages share C#'s requirement that the assignment be known at compile-time (the only other one I can find is Nim).

kazinator 10y ago
Nitpick: (scoped) const variables in C can be initialized from run-time values, not assigned. RAAI: Really, assignment ain't initialization. A file scope const object in C can have a value which is not known at the point of declaration. extern const int var; This one is not known until either a definition is supplied later in the same translation unit, or else not until linkage with another translation unit which supplies a definition. static const int var; In this case, the value is not determined until either a definition is seen which provides an initializer, or else the the end of the translation unit is reached (whereupon the tentative definition becomes actual, with a value of zero). In this situation, though, the static value can be propagated as a true literal constant into code which precedes the point where the value is known. Just not in a "one-pass compiler". This is also the case when a block-scoped const is initialized with a literal constant: { const int x = 5; /* almost "true" constant */ ... } In C, x isn't considered a constant expression, but de facto it is, which is good enough for optimizing.
nightski 10y ago
It was an exception to your blanket statement (no language uses this definition of const). Apparently the only language that you consider relevant is C, which is fine. But I wouldn't take many cues from C in reference to modern language design and proper semantics. As useful as it is C has many holes and broken semantics.

by kedean 10y ago

kazinator 10y ago

Nitpick: (scoped) const variables in C can be initialized from run-time values, not assigned. RAAI: Really, assignment ain't initialization. A file scope const object in C can have a value which is not known at the point of declaration. extern const int var; This one is not known until either a definition is supplied later in the same translation unit, or else not until linkage with another translation unit which supplies a definition. static const int var; In this case, the value is not determined until either a definition is seen which provides an initializer, or else the the end of the translation unit is reached (whereupon the tentative definition becomes actual, with a value of zero). In this situation, though, the static value can be propagated as a true literal constant into code which precedes the point where the value is known. Just not in a "one-pass compiler". This is also the case when a block-scoped const is initialized with a literal constant: { const int x = 5; /* almost "true" constant */ ... } In C, x isn't considered a constant expression, but de facto it is, which is good enough for optimizing.

nightski 10y ago

It was an exception to your blanket statement (no language uses this definition of const). Apparently the only language that you consider relevant is C, which is fine. But I wouldn't take many cues from C in reference to modern language design and proper semantics. As useful as it is C has many holes and broken semantics.