digitalmars.D.bugs - [Issue 4761] New: std.array.mul()
- d-bugmail puremagic.com (56/61) Aug 29 2010 http://d.puremagic.com/issues/show_bug.cgi?id=4761
- d-bugmail puremagic.com (11/11) Aug 29 2010 http://d.puremagic.com/issues/show_bug.cgi?id=4761
- d-bugmail puremagic.com (112/112) Sep 01 2010 http://d.puremagic.com/issues/show_bug.cgi?id=4761
http://d.puremagic.com/issues/show_bug.cgi?id=4761
Summary: std.array.mul()
Product: D
Version: D2
Platform: All
OS/Version: All
Status: NEW
Keywords: patch
Severity: enhancement
Priority: P2
Component: Phobos
AssignedTo: nobody puremagic.com
ReportedBy: bearophile_hugs eml.cc
In Python I use very often the * (__mul__) list operator, it's handy in many
situations (it is not lazy):
"abc" * -1
''
"abc" * 0
''
"abc" * 1
'abc'
"abc" * 5
'abcabcabcabcabc'
[0] * 5
[0, 0, 0, 0, 0]
It's not a good idea to add a similar product operator to D arrays because
despite vector mult operation will probably require [] (while the mul doesn't
require it), the two are too much syntactically close, they risk being too much
bug-prone.
So I suggest to simply add this mul() to std.array (this must be eager, not a
lazy range, otherwise it's not handy for its purposes):
/// ...
T[] mul(T)(T[] items, int times) {
T[] result;
static if(!is( typeof(items) == void[] )) {
if (times > 0 && items.length > 0) {
if (items.length == 1) {
result.length = times;
result[] = items[0];
} else {
result.length = items.length * times;
for (size_t pos; pos < result.length; pos += items.length)
result[pos .. pos+items.length] = items;
}
}
}
return result;
}
// demo ----------
import std.stdio;
void main() {
auto a1 = [0].mul(10);
writeln(a1);
auto a2 = [0, 5, 10].mul(4);
writeln(a2);
}
More unittests and a ddoct on request.
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This mul() needs more work, to be used on const arrays too. If you are
interested, I may try to write this improvement.
If the given array is one of the string types, it has to call
std.string.repeat() inside.
But the second argument of std.string.repeat() must become a signed integer,
otherwise you just need repeat("ab", -1) to create a crash.
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A more general version:
import std.traits: isArray, Unqual;
/// ...
T mul(T)(T items, int times) if(isArray!T) {
alias Unqual!(typeof(items[0])) E; // dangerous?
E[] result;
static if(!is( typeof(items) == void[] )) {
if (times > 0 && items.length > 0) {
if (items.length == 1) {
result.length = times;
result[] = items[0];
} else {
result.length = items.length * times;
for (size_t pos; pos < result.length; pos += items.length)
result[pos .. pos+items.length] = items[];
}
}
}
return cast(T)result; // assumeUnique?
}
unittest {
assert("".mul(-10) == "");
assert("".mul(0) == "");
assert("".mul(1) == "");
assert("".mul(10) == "");
assert("a".mul(-10) == "");
assert("a".mul(0) == "");
assert("a".mul(1) == "a");
assert("a".mul(10) == "aaaaaaaaaa");
assert("abc".mul(-10) == "");
assert("abc".mul(0) == "");
assert("abc".mul(1) == "abc");
assert("abc".mul(4) == "abcabcabcabc");
assert(""w.mul(-10) == ""w);
assert(""w.mul(0) == ""w);
assert(""w.mul(1) == ""w);
assert(""w.mul(10) == ""w);
assert("a"w.mul(-10) == ""w);
assert("a"w.mul(0) == ""w);
assert("a"w.mul(1) == "a"w);
assert("a"w.mul(10) == "aaaaaaaaaa"w);
assert("abc"w.mul(-10) == ""w);
assert("abc"w.mul(0) == ""w);
assert("abc"w.mul(1) == "abc"w);
assert("abc"w.mul(4) == "abcabcabcabc"w);
assert(""d.mul(-10) == ""d);
assert(""d.mul(0) == ""d);
assert(""d.mul(1) == ""d);
assert(""d.mul(10) == ""d);
assert("a"d.mul(-10) == ""d);
assert("a"d.mul(0) == ""d);
assert("a"d.mul(1) == "a"d);
assert("a"d.mul(10) == "aaaaaaaaaa"d);
assert("abc"d.mul(-10) == ""d);
assert("abc"d.mul(0) == ""d);
assert("abc"d.mul(1) == "abc"d);
assert("abc"d.mul(4) == "abcabcabcabc"d);
assert((new int[0]).mul(-10) == (new int[0]));
assert((new int[0]).mul(0) == (new int[0]));
assert((new int[0]).mul(1) == (new int[0]));
assert((new int[0]).mul(10) == (new int[0]));
assert([1].mul(-10) == (new int[0]));
assert([1].mul(0) == (new int[0]));
assert([1].mul(1) == [1]);
assert([1].mul(5) == [1,1,1,1,1]);
assert([1.5,2.3,3.1].mul(-10) == (new double[0]));
assert([1.5,2.3,3.1].mul(0) == (new double[0]));
assert([1.5,2.3,3.1].mul(1) == [1.5,2.3,3.1]);
assert([1.5,2.3,3.1].mul(2) == [1.5,2.3,3.1,1.5,2.3,3.1]);
const int[] a1;
assert(a1.mul(-10) == a1);
assert(a1.mul(0) == a1);
assert(a1.mul(1) == a1);
assert(a1.mul(10) == a1);
const int[] a2 = [1];
assert(a2.mul(-10) == a1);
assert(a2.mul(0) == a1);
assert(a2.mul(1) == a2);
assert(a2.mul(5) == [1,1,1,1,1]);
const int[] a3 = [1, 2, 3];
assert(a3.mul(-10) == a1);
assert(a3.mul(0) == a1);
assert(a3.mul(1) == a3);
assert(a3.mul(4) == [1,2,3,1,2,3,1,2,3,1,2,3]);
static assert(is(typeof(a3.mul(4)) == const int[]));
immutable int[] a4;
assert(a4.mul(-10) == a4);
assert(a4.mul(0) == a4);
assert(a4.mul(1) == a4);
assert(a4.mul(10) == a4);
immutable int[] a5 = [1];
assert(a5.mul(-10) == a4);
assert(a5.mul(0) == a4);
assert(a5.mul(1) == a5);
assert(a5.mul(5) == [1,1,1,1,1]);
immutable int[] a6 = [1, 2, 3];
assert(a6.mul(-10) == a4);
assert(a6.mul(0) == a4);
assert(a6.mul(1) == a6);
assert(a6.mul(4) == [1,2,3,1,2,3,1,2,3,1,2,3]);
static assert(is(typeof(a6.mul(4)) == immutable int[]));
immutable(int)[] a7 = [1, 2, 3];
static assert(is(typeof(a7.mul(0)) == immutable(int)[]));
static assert(is(typeof(a7.mul(1)) == immutable(int)[]));
static assert(is(typeof(a7.mul(3)) == immutable(int)[]));
}
void main() {}
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