Re: String Theory Questions
On Sunday, 14 September 2014 at 00:34:56 UTC, WhatMeWorry wrote: So is one form (Empty strings versus null strings) considered better than the other? Or does it depend on the context? For all practical purposes they should be equivalent in D code. I suppose the distinction exists because somebody claimed he can make sense of it. Some API may rely on distinction between null and empty string, like XML DOM, though I don't think such interface is very useful. Also for some reason boolean value of a string is derived from ptr instead of length... meh.
Re: String Theory Questions
On Sunday, 14 September 2014 at 09:07:26 UTC, Kagamin wrote: On Sunday, 14 September 2014 at 00:34:56 UTC, WhatMeWorry wrote: So is one form (Empty strings versus null strings) considered better than the other? Or does it depend on the context? For all practical purposes they should be equivalent in D code. I suppose the distinction exists because somebody claimed he can make sense of it. Some API may rely on distinction between null and empty string, like XML DOM, though I don't think such interface is very useful. Also for some reason boolean value of a string is derived from ptr instead of length... meh. Which makes sense given the distinction exists, IMO. Compare for example with Ruby, where empty strings and `0` integers also evaluate to true, but only `nil` and `false` evaluated to false.
Re: String Theory Questions
On Sun, 14 Sep 2014 09:07:25 + Kagamin via Digitalmars-d-learn digitalmars-d-learn@puremagic.com wrote: Also for some reason boolean value of a string is derived from ptr instead of length... meh. for the reason that all reference objects either null or non-null. empty string is non-null, so... it's C leftover actually. there are alot such leftovers in D. signature.asc Description: PGP signature
Re: String Theory Questions
On 9/14/2014 2:09 AM, WhatMeWorry wrote: The name string is aliased to immutable(char)[] Why was immutable chosen? Why not mutable. Or why not just make another alias called strung where it is aliased to mutable(char)[] If you want a mutable array of characters, just use char[]. --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com
Re: String Theory Questions
On Saturday, 13 September 2014 at 23:21:09 UTC, David Nadlinger wrote: On Saturday, 13 September 2014 at 22:41:39 UTC, AsmMan wrote: D string are actullay C-strings? No. But string *literals* are guaranteed to be 0-terminated for easier interoperability with C code. David ah makes sense. On Sunday, 14 September 2014 at 12:07:16 UTC, Marc Schütz wrote: On Sunday, 14 September 2014 at 09:07:26 UTC, Kagamin wrote: On Sunday, 14 September 2014 at 00:34:56 UTC, WhatMeWorry wrote: So is one form (Empty strings versus null strings) considered better than the other? Or does it depend on the context? For all practical purposes they should be equivalent in D code. I suppose the distinction exists because somebody claimed he can make sense of it. Some API may rely on distinction between null and empty string, like XML DOM, though I don't think such interface is very useful. Also for some reason boolean value of a string is derived from ptr instead of length... meh. Which makes sense given the distinction exists, IMO. Compare for example with Ruby, where empty strings and `0` integers also evaluate to true, but only `nil` and `false` evaluated to false. That's why I don't like most of dynamic languages... type system is a mess. I don't like even the fact one can do: x = abc; f(x) x = 10; g(x); and it work
Re: String Theory Questions
On Sunday, 14 September 2014 at 13:48:01 UTC, ketmar via Digitalmars-d-learn wrote: for the reason that all reference objects either null or non-null. empty string is non-null, so... it's C leftover actually. there are alot such leftovers in D. For pointers it's logical, but it doesn't work as good for slices: they're better thought of as either empty or non-empty.
String Theory Questions
The name string is aliased to immutable(char)[] Why was immutable chosen? Why not mutable. Or why not just make another alias called strung where it is aliased to mutable(char)[] Also, since strings are arrays and arrays are structs with a length and ptr field, I ran the following code for both an empty string and a null string. string emptyStr = ; writeln(emptyStr.ptr is , emptyStr.ptr); writeln(emptyStr.length is , emptyStr.length); string nullStr = null; writeln(nullStr.ptr is , nullStr.ptr); writeln(nullStr.length is , nullStr.length); and got the following results: emptyStr.ptr is 42F080 emptyStr.length is 0 nullStr.ptr is null nullStr.length is 0 I guess I was expecting them to be equivalent. I can understand why both lengths are zero. But what is emptyStr.ptr doing with the 42F080 value? I presume this is a address? If so, what does this address contain and what is it used for? Or maybe a more succinct question is why not just set emptyStr.ptr to null and be done with it?
Re: String Theory Questions
On Sat, 13 Sep 2014 17:09:56 +
WhatMeWorry via Digitalmars-d-learn digitalmars-d-learn@puremagic.com
wrote:
I guess I was expecting them to be equivalent. I can understand
why both lengths are zero. But what is emptyStr.ptr doing with
the 42F080 value? I presume this is a address? If so, what does
this address contain and what is it used for?
it's used to keep empty string. ;-)
note that null string and empty string aren't same things. arrays
are reference types and compiler magically knows that null-arrays are
just empty arrays (and you can assign 'null' to array to clear it).
but strings are special in one funny way: when compiler sees string
literal (i.e. quoted string) in source code, it actually generates
C-like zero-terminated string. this is to ease C interop, so we can
call C functions like this: `printf(my string!\n);` instead of this:
`printf(my string!\n.toStringz);`.
so your empty string is actually points to zero byte (and has zero
length, 'cause D strings aren't zero-terminated). and null string is
really null, i.e. contains no data.
as for immutable: it is done this way so compiler can place string
literals in read-only section of resulting binary. without immutability
calling `void foo (string s);` as `foo(wow!)` will require copying
string to heap first ('cause `s` contents allowed to be changed in
`foo()`).
adding implicit copy-on-writing semantic will increase compiler
complexity and hidden dynamic array struct size for virtually nothing.
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Re: String Theory Questions
On Saturday, 13 September 2014 at 17:31:18 UTC, ketmar via Digitalmars-d-learn wrote: On Sat, 13 Sep 2014 17:09:56 + WhatMeWorry via Digitalmars-d-learn digitalmars-d-learn@puremagic.com wrote: I guess I was expecting them to be equivalent. I can understand why both lengths are zero. But what is emptyStr.ptr doing with the 42F080 value? I presume this is a address? If so, what does this address contain and what is it used for? it's used to keep empty string. ;-) note that null string and empty string aren't same things. arrays are reference types and compiler magically knows that null-arrays are just empty arrays (and you can assign 'null' to array to clear it). but strings are special in one funny way: when compiler sees string literal (i.e. quoted string) in source code, it actually generates C-like zero-terminated string. this is to ease C interop, so we can call C functions like this: `printf(my string!\n);` instead of this: `printf(my string!\n.toStringz);`. D string are actullay C-strings?
Re: String Theory Questions
On Sat, 13 Sep 2014 22:41:38 + AsmMan via Digitalmars-d-learn digitalmars-d-learn@puremagic.com wrote: D string are actullay C-strings? in no way. only string *LITERALS* are zero-terminated. signature.asc Description: PGP signature
Re: String Theory Questions
On Saturday, 13 September 2014 at 22:41:39 UTC, AsmMan wrote: D string are actullay C-strings? No. But string *literals* are guaranteed to be 0-terminated for easier interoperability with C code. David
Re: String Theory Questions
On Saturday, 13 September 2014 at 23:22:40 UTC, ketmar via Digitalmars-d-learn wrote: On Sat, 13 Sep 2014 22:41:38 + AsmMan via Digitalmars-d-learn digitalmars-d-learn@puremagic.com wrote: D string are actullay C-strings? in no way. only string *LITERALS* are zero-terminated. Ok. So I wrote the following: char c = *(emptyStr.ptr); if (c == '\0') writeln(emptyStr only consists of an end of line character); and sure enough, the writeln() was executed. Ok, So an empty string has a pointer which just points to C's end of line character. So is one form (Empty strings versus null strings) considered better than the other? Or does it depend on the context? Also as an aside (and I'm not trying to be flippant here), aren't all strings literals? I mean, can someone give me an example of a string non-literal?
Re: String Theory Questions
On Sun, 14 Sep 2014 00:34:54 +
WhatMeWorry via Digitalmars-d-learn digitalmars-d-learn@puremagic.com
wrote:
So is one form (Empty strings versus null strings) considered
better than the other? Or does it depend on the context?
one is better than another in the sense that blue is better than green
(or vice versa). ;-)
don't count on that trailing zero, and don't count on empty string
being null or points to somewhere. `.length` is all that matters.
Also as an aside (and I'm not trying to be flippant here), aren't
all strings literals? I mean, can someone give me an example of
a string non-literal?
string foo () {
import std.conv;
string s;
foreach (i; 0..10) s ~= to!string(i);
return s;
}
this function returns string, but that string is in no way built
from literal.
note that it's string *contents* are immutable, not the whole string
structure. there is a difference between `immutable(char[])` and
`immutable(char)[]`. that is why you can use `~=` on strings.
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Re: String Theory Questions
On 09/13/2014 05:34 PM, WhatMeWorry wrote: aren't all strings literals? Literals are values that are typed as is in source code: http://en.wikipedia.org/wiki/Literal_%28computer_programming%29 Ali
