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digitalmars.D - Simple IFTI use

reply Kevin Bealer <Kevin_member pathlink.com> writes:
Often when working with D arrays, I miss the "doubling" effect of push_back from
C++ std::vector.  With IFTI, this is possible (trivial, really) in D.  I put
some code here - the idea is to use existing arrays, no special classes, but
have an "append" functionality, like vector::push_back().

: // -*- c++ -*-
:
: import std.string;
:
: template push_back(T) {
:     // The first arg is inout only for performance reasons.
:
:     void push_back(inout T elem, inout T[] vec, inout int vsize)
:     {
:         assert(vec.length >= vsize);
:
:         if (vec.length != vsize) {
:             vec.length = (vec.length
:                           ? vec.length * 2
:                           : 4); // arbitrary
:         }
:
:         vec[vsize++] = elem;
:     }
: };
:
: // Usage
:
: import simplevec;
:
: Foo[] stuff; int stuff_size;
:
: Foo f = new Foo;
:
: push_back(f, stuff, stuff_size);

Kevin
Apr 02 2006
parent reply Sean Kelly <sean f4.ca> writes:
Kevin Bealer wrote:
 Often when working with D arrays, I miss the "doubling" effect of push_back
from
 C++ std::vector.  With IFTI, this is possible (trivial, really) in D.  I put
 some code here - the idea is to use existing arrays, no special classes, but
 have an "append" functionality, like vector::push_back().
 
 : // -*- c++ -*-
 :
 : import std.string;
 :
 : template push_back(T) {
 :     // The first arg is inout only for performance reasons.
 :
 :     void push_back(inout T elem, inout T[] vec, inout int vsize)
 :     {
 :         assert(vec.length >= vsize);
 :
 :         if (vec.length != vsize) {
 :             vec.length = (vec.length
 :                           ? vec.length * 2
 :                           : 4); // arbitrary
 :         }
 :
 :         vec[vsize++] = elem;
 :     }
 : };
 :
 : // Usage
 :
 : import simplevec;
 :
 : Foo[] stuff; int stuff_size;
 :
 : Foo f = new Foo;
 :
 : push_back(f, stuff, stuff_size);

If you flip the parameters: void push_back( inout T[] vec, T elem ) The array trick could be used to call it like so: f.push_back( stuff ); This would obviously also require an overload that doesn't take a third parameter. Sean
Apr 02 2006
parent Kevin Bealer <Kevin_member pathlink.com> writes:
In article <e0qcfd$24m3$1 digitaldaemon.com>, Sean Kelly says...
Kevin Bealer wrote:
 Often when working with D arrays, I miss the "doubling" effect of push_back
from
 C++ std::vector.  With IFTI, this is possible (trivial, really) in D.  I put
 some code here - the idea is to use existing arrays, no special classes, but
 have an "append" functionality, like vector::push_back().
 
 : // -*- c++ -*-
 :
 : import std.string;
 :
 : template push_back(T) {
 :     // The first arg is inout only for performance reasons.
 :
 :     void push_back(inout T elem, inout T[] vec, inout int vsize)
 :     {
 :         assert(vec.length >= vsize);
 :
 :         if (vec.length != vsize) {
 :             vec.length = (vec.length
 :                           ? vec.length * 2
 :                           : 4); // arbitrary
 :         }
 :
 :         vec[vsize++] = elem;
 :     }
 : };
 :
 : // Usage
 :
 : import simplevec;
 :
 : Foo[] stuff; int stuff_size;
 :
 : Foo f = new Foo;
 :
 : push_back(f, stuff, stuff_size);

If you flip the parameters: void push_back( inout T[] vec, T elem ) The array trick could be used to call it like so: f.push_back( stuff ); This would obviously also require an overload that doesn't take a third parameter. Sean

There is a related definition that I've used that does not require a seperate length primitive... it looks like this (I've flipped the args too): : void push_back(inout T[] vec, inout T elem) : { : int vsize = vec.length; : : if (! (vsize & (vsize-1))) { : vec.length = vsize * 2; : } : vec.length = vsize+1; : vec[$-1] = elem; : } The (vsize & (vsize-1)) tests for powers of two, so this doubles the capacity of the array whenever length is 2, 4, 8, etc, and an element is added. The length is then reduced back to one more than the previous length. The rest of the time it just bumps .length by 1, which won't reallocate since the capacity has been previously bumped. The only hitch is, if you start with an array of length 70, this version can't tell and will not do the capacity trick till you get to 128. This won't matter though if you use this template for all of the operations. Kevin
Apr 03 2006