digitalmars.D.learn - How to get hash value of an object?
- panmengh (86/86) Nov 26 2016 How to get hash value of an object?
- Steven Schveighoffer (9/12) Nov 28 2016 hashOf is kind of this horrible hacky thing that nobody should be using....
- Era Scarecrow (13/17) Dec 04 2016 Ugg... Anything with pointers, classes or arrays will have huge
- Seb (4/12) Dec 11 2016 For the record: it was a regression and has been fixed with
How to get hash value of an object?
Use hashOf? or typeid(T).getHash(&o)?
I test with the following code:
System:
windows 10
dmd --version
DMD32 D Compiler v2.072.0 (official download version)
ldc2 --version
LDC - the LLVM D compiler (1.1.0git-62a2252) (the latest git
master version)
based on DMD v2.071.2 and LLVM 3.9.1git
import std.stdio;
void main()
{
string[string] a;
string[string] b0;
writeln(a.hashOf(), "\t\t",typeid(typeof(a)).getHash(&a),
"\t\t\t",
b0.hashOf(), "\t\t",typeid(typeof(b0)).getHash(&b0), "
", a,);
a["1"] = "1";
string[string] b1 = ["1":"1"];
writeln(a.hashOf(), "\t\t",typeid(typeof(a)).getHash(&a),
"\t\t",
b1.hashOf(), "\t\t",typeid(typeof(b1)).getHash(&b1), "
", a,);
a["9"] = "9";
string[string] b2 = ["1":"1", "9":"9"];
writeln(a.hashOf(), "\t\t",typeid(typeof(a)).getHash(&a),
"\t\t\t",
b2.hashOf(), "\t\t",typeid(typeof(b2)).getHash(&b2), "
", a,);
a["3"] = "3";
string[string] b3 = ["1":"1", "9":"9", "3":"3"];
writeln(a.hashOf(), "\t\t",typeid(typeof(a)).getHash(&a),
"\t\t",
b3.hashOf(), "\t\t",typeid(typeof(b3)).getHash(&b3), "
", a,);
a.remove("1");
a["1"] = "1";
string[string] b4 = ["1":"1", "9":"9", "3":"3"];
writeln(a.hashOf(), "\t\t",typeid(typeof(a)).getHash(&a),
"\t\t",
b3.hashOf(), "\t\t",typeid(typeof(b4)).getHash(&b4), "
", a,);
}
Output:
dub --compiler=dmd -a=x86_64
Running .\test2.exe
1669671676 0 1669671676 0 []
732702303 2197205690 683765274 3388425732 ["1":"1"]
732702303 0 912895782 0 ["1":"1",
"9":"9"]
732702303 2197205690 4139255736 3388425732 ["3":"3",
"1":"1", "9":"9"]
732702303 2197205690 4139255736 3388425732 ["3":"3",
"1":"1", "9":"9"]
test2.exe (second run)
1669671676 0 1669671676 0 []
1608602074 122060002 2487796584 31054674 ["1":"1"]
1608602074 0 3256818953 0 ["1":"1",
"9":"9"]
1608602074 122060002 667025292 31054674 ["3":"3",
"1":"1", "9":"9"]
1608602074 122060002 667025292 31054674 ["3":"3",
"1":"1", "9":"9"]
dub --compiler=ldc2 -a=x86_64
Running .\test2.exe
593689054 0 593689054 0 []
1747365348 1899073920 1747365348 1899073920 ["1":"1"]
3252326176 0 3252326176 0 ["1":"1",
"9":"9"]
492636279 1899073920 492636279 1899073920 ["3":"3",
"1":"1", "9":"9"]
492636279 1899073920 492636279 1899073920 ["3":"3",
"1":"1", "9":"9"]
test2.exe (second run)
593689054 0 593689054 0 []
1747365348 2353409518 1747365348 2353409518 ["1":"1"]
3252326176 0 3252326176 0 ["1":"1",
"9":"9"]
492636279 2353409518 492636279 2353409518 ["3":"3",
"1":"1", "9":"9"]
492636279 2353409518 492636279 2353409518 ["3":"3",
"1":"1", "9":"9"]
Does only hashOf with ldc2 return the right value?
Nov 26 2016
On 11/27/16 2:10 AM, panmengh wrote:How to get hash value of an object? Use hashOf? or typeid(T).getHash(&o)?hashOf is kind of this horrible hacky thing that nobody should be using. It literally takes whatever you pass it and hashes the local bytes. It doesn't care about opHash or if any of those bytes are actually references to the things you want hashed. In fact, for class references, it just hashes the bytes that point at the class. Useless. Long story short, use typeid(T).getHash(&o).Does only hashOf with ldc2 return the right value?If it does, that's a coincidence. Happened to allocate in the same place. -Steve
Nov 28 2016
On Tuesday, 29 November 2016 at 00:05:31 UTC, Steven Schveighoffer wrote:hashOf is kind of this horrible hacky thing that nobody should be using. It literally takes whatever you pass it and hashes the local bytes.Ugg... Anything with pointers, classes or arrays will have huge problems with consistency; While anything with fixed static arrays or pure value-types will result in proper values. I'd almost prefer an option to get hashOf all inner object types and then xor them all together. Although this could make for a very complex hashOf depending on implementation of the object.Long story short, use typeid(T).getHash(&o).Hmmm maybe make any struct have hashOf disabled if it includes any pointers or dynamic arrays or inner objects that can't get a proper hash of it. While it will break things, at least you know what can't be hashed when you try to use it. Or maybe have that as a compiler option for those wanting to make use of that.
Dec 04 2016
Seb <seb wilzba.ch> On Sunday, 4 December 2016 at 13:17:09 UTC, Era Scarecrow wrote:On Tuesday, 29 November 2016 at 00:05:31 UTC, Steven Schveighoffer wrote:For the record: it was a regression and has been fixed with https://github.com/dlang/druntime/pull/1707 and thus should be part of the next point release.hashOf is kind of this horrible hacky thing that nobody should be using. It literally takes whatever you pass it and hashes the local bytes.Ugg... Anything with pointers, classes or arrays will have huge problems with consistency; While anything with fixed static arrays or pure value-types will result in proper values.
Dec 11 2016