www.digitalmars.com         C & C++   DMDScript  

digitalmars.D - Built-in arrays as output ranges

reply Steve Teale <steve.teale britseyeview.com> writes:
Not a bug, but would it be reasonable to expand a little on the documentation
for an output range, perhaps along the lines:

r.put(e) puts e in the range (in a range-dependent manner) and advances to the
popFront position in the range. Successive calls to r.put add elements to the
range. put may throw to signal failure.

When using a built-in array as an output range, to do anything useful it is
necessary to take a reference to the original array before using put. The
original array will be nibbled away by put operations (see std.array). For
example:

    int[] a = [ 1,2,3 ];
    int[] b = a;
    a.put(-a[0]);
    a.put(-a[0]);
    writefln("([%s] [%s]", b, a);
   // [ -1, -2, 3] [ 3 ]
Feb 07 2010
parent reply Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:
Steve Teale wrote:
 Not a bug, but would it be reasonable to expand a little on the documentation
for an output range, perhaps along the lines:
 
 r.put(e) puts e in the range (in a range-dependent manner) and advances to the
popFront position in the range. Successive calls to r.put add elements to the
range. put may throw to signal failure.
 
 When using a built-in array as an output range, to do anything useful it is
necessary to take a reference to the original array before using put. The
original array will be nibbled away by put operations (see std.array). For
example:
 
     int[] a = [ 1,2,3 ];
     int[] b = a;
     a.put(-a[0]);
     a.put(-a[0]);
     writefln("([%s] [%s]", b, a);
    // [ -1, -2, 3] [ 3 ]

Right. Speaking of which, I think it's sensible to always leave the test for empty range in, even in release unsafe builds. void put(T, E)(ref T[] range, E element) if (!isSomeString!(T[])) { enforce(!range.empty, "Attempting to put in an empty array"); *range.ptr = element; range.popFront(); } enforce() will never be disabled. As an aside, I just realized I haven't implemented put for strings yet, and also that I'd promised a check in this weekend. Andrei
Feb 07 2010
parent reply Steve Teale <steve.teale britseyeview.com> writes:
 
 enforce() will never be disabled.
 
 As an aside, I just realized I haven't implemented put for strings yet,
 and also that I'd promised a check in this weekend.
 
 
 Andrei

Actually, thinking about this overnight, I'm a bit unhappy about giving the impression that a built-in array can serve as an output range. It really isn't true unless you never want to see the output again. If you do, some data structure is required, either a loose combination of an array and an unprotected reference to its original state (arrays a and b), or something more explicit like: struct arrayOutputRange(T) { T[] array; uint pos; this(uint sx) { ... } void put(T val) { ... } } Steve
Feb 07 2010
parent Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:
Steve Teale wrote:
 enforce() will never be disabled.

 As an aside, I just realized I haven't implemented put for strings yet,
 and also that I'd promised a check in this weekend.


 Andrei

Actually, thinking about this overnight, I'm a bit unhappy about giving the impression that a built-in array can serve as an output range. It really isn't true unless you never want to see the output again. If you do, some data structure is required, either a loose combination of an array and an unprotected reference to its original state (arrays a and b), or something more explicit like: struct arrayOutputRange(T) { T[] array; uint pos; this(uint sx) { ... } void put(T val) { ... } } Steve

copy(source, target) does make sense for arrays as output ranges. Since target is passed by value, your copy will see what's been copied. Andrei
Feb 08 2010