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digitalmars.D.bugs - [Issue 9408] New: invariant should be non-const by default and settable to const

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=9408

           Summary: invariant should be non-const by default and settable
                    to const
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: andrej.mitrovich gmail.com
        ReportedBy: andrej.mitrovich gmail.com



21:08:35 PST ---
class C1
{
    int x;
    invariant() const
    {
        x = 1;   // not ok
    }
}

class C2
{
    int x;
    invariant()
    {
        x = 1;  // ok
    }
}

See also https://github.com/D-Programming-Language/dmd/pull/1073,
and discussion http://forum.dlang.org/thread/jvh87s%241gl6%241 digitalmars.com

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next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=9408




21:45:00 PST ---
https://github.com/D-Programming-Language/dmd/pull/1560

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prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=9408


Walter Bright <bugzilla digitalmars.com> changed:

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                 CC|                            |bugzilla digitalmars.com



11:20:58 PST ---
I think this change is a step backwards.

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prev sibling parent d-bugmail puremagic.com writes:
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bearophile_hugs eml.cc changed:

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                 CC|                            |bearophile_hugs eml.cc





 I think this change is a step backwards.


I think in this discussion there are two main sides:

Some people want to write D code right now, so they don't want to fight too
much with problems caused by const. And they like "freedom". Often this side is
also associated with the "worse is better" language design philosophy.

They other camp reads the texts written by the creator of the Eiffel language,
that explain what Contracts are and what they are meant to. For them a
precondition or an invariant should never modify the state of the struct/class.
And the language should enforce this, to avoid bugs. They accept less a bit
less convenience for stronger guarantees and "cleaner" code.
Mathematics-oriented people are often on this side.

D language has introduced const/invariant, but it's so strong that sometimes
you don't want or your can't use it. So sometimes D programmers don't want to
eat their own dog food.

I generally prefer a more "clean" style of coding, because from experience I
have seen that the amount of time wasted making a fussy type system happy, is
often paid later in less bugs, that otherwise waste far more of my time.

But in the end I sympathize with both camps, for different reasons. Both are
partially right. In the end a static analysis tool can just enforce all
invariants to be tagged with "const", so the end result is not too much
different.

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