http://d.puremagic.com/issues/show_bug.cgi?id=5555

           Summary: built-in associative array's length is nothrow
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P3
         Component: druntime
        AssignedTo: nobody@puremagic.com
        ReportedBy: repeatedly@gmail.com


--- Comment #0 from Masahiro Nakagawa <repeatedly@gmail.com> 2011-02-09 08:35:27 PST ---
I have following code:

    // aa is a string[string];
    nothrow bool empty() const
    {
        return aa.length == 0;
    }

I want use this code but dmd fails.

    Error: function hoge.Foo.empty 'empty' is nothrow yet may throw

built-in AA's length() depends on _aaLen in rt/aaA.d.
I think these functions should be nothrow.

This issue breaks my template engine API ;(

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bearophile_hugs@eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bearophile_hugs@eml.cc


--- Comment #1 from bearophile_hugs@eml.cc 2011-02-09 09:48:44 PST ---
There is a similar problem with pure too:


int[int] aa;
nothrow int foo() {
    return aa.length;
}
pure int bar() {
    int[int] aa2;
    return aa2.length;
}
void main() {}

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bearophile_hugs@eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|built-in associative        |Built-in associative arrays
                   |array's length is not       |in pure nothrow functions
                   |nothrow                     |


--- Comment #2 from bearophile_hugs@eml.cc 2011-09-18 11:39:35 PDT ---
Currently associative arrays can't be used much in pure nothrow functions:

void main() pure nothrow {
    int[int] aa;
    aa.rehash;
    auto L = aa.length;
    auto x = aa.get(0, 10);
    auto k = aa.keys;
    auto v = aa.values;
    auto bk = aa.byKey();
    auto bv = aa.byValue();
}


DMD 2.055 gives:

test.d(3): Error: pure function 'main' cannot call impure function 'rehash'
test.d(4): Error: pure function 'main' cannot call impure function 'length'
test.d(5): Error: pure function 'main' cannot call impure function 'get'
test.d(6): Error: pure function 'main' cannot call impure function 'keys'
test.d(7): Error: pure function 'main' cannot call impure function 'values'
test.d(8): Error: pure function 'main' cannot call impure function 'byKey'
test.d(9): Error: pure function 'main' cannot call impure function 'byValue'
test.d(3): Error: aa.rehash is not nothrow
test.d(4): Error: aa.length is not nothrow
test.d(5): Error: aa.get is not nothrow
test.d(6): Error: aa.keys is not nothrow
test.d(7): Error: aa.values is not nothrow
test.d(8): Error: aa.byKey is not nothrow
test.d(9): Error: aa.byValue is not nothrow
test.d(1): Error: function D main 'main' is nothrow yet may throw

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Witold Baryluk <baryluk@smp.if.uj.edu.pl> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |baryluk@smp.if.uj.edu.pl


--- Comment #3 from Witold Baryluk <baryluk@smp.if.uj.edu.pl> 2012-07-05 11:25:55 PDT ---
Any updates? I'm trying to implement toHash() method which needs to be nothrow, and inside it I use aa.byKey or aa.keys or foreach (...; aa). Currently I cannot without some hacks. Fixes in rt.* should be relatively easy for most of this functions.

Regards,
Witek

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lt.infiltrator@gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |lt.infiltrator@gmail.com


--- Comment #4 from lt.infiltrator@gmail.com 2012-12-18 17:13:09 PST ---
*** Issue 9168 has been marked as a duplicate of this issue. ***

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w0rp <moebiuspersona@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |moebiuspersona@gmail.com


--- Comment #5 from w0rp <moebiuspersona@gmail.com> 2013-04-18 00:27:40 PDT ---
I'd like to remind everyone of this issue. I hold a strong belief that even if the internals of associative arrays are impure, unsafe, and may throw, properties for associative arrays should "lie" about these things because they are invaluable mechanisms for implementing so many pure, @safe, and nothrow algorithms.

They aren't really pure because they modify global state, but so does allocating memory, which pure allows for.

They aren't @safe, because they rely on certain memory techniques, but these are internals that form the language.

They aren't nothrow, because checking the properties of an associative array may fail, but this is as much of an unrecoverable error as an OutOfMemoryError.

If the properties of associative arrays take on all of these things, it would make it possible to create an entire host of code which is pure, @safe, and nothrow. (For starters, I can imagine undirected and directed graph types which meet these requirements.)

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