Re: opEquals nothrow
On Thursday, 20 July 2017 at 15:10:24 UTC, Aldo wrote:
On Thursday, 20 July 2017 at 14:59:50 UTC, Steven Schveighoffer
wrote:
On 7/20/17 10:38 AM, Aldo wrote:
Hello,
im tring to add nothrow keyword in my code, but compilation
fails :
function 'object.opEquals' is not nothrow
its a simple comparison between 2 objects. How to make
opEquals nothrow ?
You can't. Object.opEquals is not nothrow, so object.opEquals
is not nothrow (note the former is the virtual member
function, the latter is a global function which is what the
compiler actually calls).
It is a legacy limitation. Until we get rid of all the Object
base methods for things like opEquals and toHash, we will not
be able to fix this.
-Steve
Im using DerelictGLFW3, to process events im doing this :
glfwSetMouseButtonCallback(window, );
onMouseClick function must be nothrow.
But now I can't do anything in this function because I can't
convert my code to nothrow.
Can I put a try catch in the body ?
extern(C) nothrow
{
void onMouseClick(GLFWwindow* window, int button, int
action, int d)
{
try
{
// my code
}
catch
{
}
}
}
it seems its working but what about performances ?
thanks
You could also try assumeWontThrow.
https://dlang.org/library/std/exception/assume_wont_throw.html
Re: Possible to write a classic fizzbuzz example using a UFCS chain?
On Tuesday, 28 April 2015 at 10:46:54 UTC, Gary Willoughby wrote:
After reading the following thread:
http://forum.dlang.org/thread/nczgumcdfystcjqyb...@forum.dlang.org
I wondered if it was possible to write a classic fizzbuzz[1]
example using a UFCS chain? I've tried and failed.
[1]: http://en.wikipedia.org/wiki/Fizz_buzz
You can do this.
import std.range : iota;
import std.algorithm : map, each;
import std.typecons : Tuple, tuple;
import std.stdio : writeln;
Tuple!(size_t, string) fizzbuzz(size_t number) {
if (number % 3 == 0) {
if (number % 5 == 0) {
return tuple(number, fizzbuzz);
} else {
return tuple(number, fizz);
}
} else if (number % 5 == 0) {
return tuple(number, buzz);
}
return tuple(number, );
}
void main(string[] argv) {
iota(1, 101)
.map!fizzbuzz
.each!(x = writeln(x[0], : , x[1]));
}
The desired output may vary, depending on variations of FizzBuzz.
(Some want the number always in the output, some don't.) You
could maybe do crazy ternary expressions instead of writing a
function, or put it directly in there as a lambda, but both just
look ugly, and you might as well just write a function for it.
Re: Static if to compare two types are the exact same
On Tuesday, 7 April 2015 at 06:37:50 UTC, Jonathan wrote: static if (is(T == V)) Are static ifs always checked outside of runtime? Is it possible for a static if condition to be undeterminable outside of runtime, or would such a condition throw a compiler error? 'static if' is always run at compile time, so it needs access to compile time information. Fortunately, you can access quite a lot at compile time in D.
Re: Binary search in structs
On Sunday, 5 April 2015 at 23:06:27 UTC, FreeSlave wrote:
I have array of structs sorted by specific field. How can I
perform binary search using this field as a key?
Currently I ended up with this, but it gives error:
struct S
{
int i;
string s;
}
import std.range;
void main(string [] args)
{
S[] structs = [{1,hello}, {2,world}, {3, !}];
//sorted by i
auto sortedRange = assumeSorted!(function bool(ref const S
item, int needle) {
return item.i needle;
})(structs);
sortedRange.trisect(2); //compilation error
}
I believe you have to pass trisect a value of S. So S(2, )
would do here, I suppose.
Re: @trusted and return ref
On Wednesday, 25 February 2015 at 06:48:17 UTC, Ola Fosheim Grøstad wrote: On Tuesday, 24 February 2015 at 22:49:17 UTC, w0rp wrote: In general, @trusted means I have proven myself that this code is actually safe, eeven though it uses unsafe features. The compiler has to be pessimistic and assume that everything which can be used unsafely will be used unsafely. @trusted, as it is used here, is used to say, I assure you I have used this in a safe manner. From http://dlang.org/function.html#trusted-functions : «Trusted functions are guaranteed by the programmer to not exhibit any undefined behavior if called by a safe function.» I take this to mean that anything that is wrapped up in @trusted should not violate memory safety when in injected into any arbitrary context marked as @safe. The key phrase is guaranteed by the programmer. Which means that the programmer, not the compiler, is providing a guarantee that calling a @trusted function will not violate memory safety. If the programmer cannot make that guarantee, the function should be marked as @system instead. It's a mechanism which allows humans to achieve something the compiler isn't capable of achieving, at least at this point in time. Much in the same way that a compiler cannot prove in general that programs will terminate, it can be very difficult for a compiler to prove that your program will not violate memory safety when the language is capable of calling into C code, etc. If you don't have an annotation like @trusted, the amount of code which could be run from @safe functions would be very small indeed.
Re: @trusted and return ref
On Tuesday, 24 February 2015 at 22:37:58 UTC, Ola Fosheim Grøstad wrote: If this is careful use of @trusted, then I don't see the point of having @trusted at all. What is the purpose? What is it meant to cover? In order for @trusted to make sense in this code segment ( http://dpaste.dzfl.pl/f3d854feede9 ) I would say that the whole class will have to be marked @trusted. Is that possible? In general, @trusted means I have proven myself that this code is actually safe, eeven though it uses unsafe features. The compiler has to be pessimistic and assume that everything which can be used unsafely will be used unsafely. @trusted, as it is used here, is used to say, I assure you I have used this in a safe manner. I would like to see @trusted blocks, although I can see Andrei's argument of not making it easy to do intentionally.
Re: dmd dub from git master
I hit this myself also. I was trying to use the master branch DMD, druntime, and phobos with a recent vibe.d for building the documentation with ddox, and I ran into the reliance on std.metastrings.
Re: '!' and naming conventions
On Wednesday, 18 June 2014 at 20:55:36 UTC, cym13 wrote: Hello, I see a lot of functions and other stuff with a '!' in the name such as 'bitfields!' or 'ctRegex!'. What does it mean exactly? In scheme, we use such a convention to warn that a function is not pure, but I don't see the point of using it that way in D as there are other way to express it. Moreover, I'm looking for a style guide of D, something like the PEP8 for python. Is there anything like that? Thanks! ! is actually the way in D of passing compile time arguments. So take for example the 'to' function. double foo = 3.14; // Convert a double to a string. string bar = foo.to!string; // Same as the above, written a little differently. bar = to!(string)(foo); // How C++ and friends would write it. // bar = tostring(foo);
Creating ranges over mutable, const, or immutable data structures.
I have been writing my own hashmap which can provide forward ranges usable in @safe pure nothrow functions, because it's going to be useful for creating graph data structures with the same. I came to writing my ranges and I figured out how to do everything right for just mutable hashmaps, but I have no idea how to manage the tail-const nature of ranges in a variety of combinations. I figured out that I need to satisfy the following constraints. Create a mutable KeyRange over a map which forwards on the right constness for the key type, so the following must be true. HashMap!(K, V).keys.front - K const(HashMap!(K, V)).keys.front - const(K) immutable(HashMap!(K, V)).keys.front - immutable(K) I have encounted some difficulty in trying to write a range which does this.
Re: Creating ranges over mutable, const, or immutable data structures.
On Saturday, 24 May 2014 at 18:01:43 UTC, Ali Çehreli wrote: On 05/24/2014 10:02 AM, w0rp wrote: I have been writing my own hashmap which can provide forward ranges usable in @safe pure nothrow functions, because it's going to be useful for creating graph data structures with the same. I came to writing my ranges and I figured out how to do everything right for just mutable hashmaps, but I have no idea how to manage the tail-const nature of ranges in a variety of combinations. I figured out that I need to satisfy the following constraints. Create a mutable KeyRange over a map which forwards on the right constness for the key type, so the following must be true. HashMap!(K, V).keys.front - K const(HashMap!(K, V)).keys.front - const(K) immutable(HashMap!(K, V)).keys.front - immutable(K) I have encounted some difficulty in trying to write a range which does this. How timely! :) Jonathan Crapuchettes talked about facing the same issue in his talk at DConf. Perhaps he will post his WrapMutability template here or you can wait for his talk on YouTube. Ali I thought someone would say something like that! I'll wait for the talk I suppose.
Re: Array!T and find are slow
On Saturday, 17 May 2014 at 20:06:03 UTC, Jonathan M Davis via Digitalmars-d-learn wrote: But I think that the correct solution is to improve the compiler with regards to lazy. The fact that lazy is so slow is a serious problem, and enforce is just one manifestation of it (albeit the worst because of how often it's used). - Jonathan M Davis I haven't been bitten by the performance of lazy myself, but I'd +1 that, because of how easy it can make writing code.
Re: What does it mean for opCmp and opEquals to be consistent?
On Thursday, 3 April 2014 at 10:42:33 UTC, monarch_dodra wrote: A correctly implemented AA would use opCmp to store objects in each bucket in cases of hash collisions, but still use opEqual in case of equivalence. I would add to that, try to use opCmp if it is available. It should be possible to hash something if it has toHash and opEquals, and not require opCmp for hashing.
Re: How to repeat a function call?
tuples are definitely a compile-time job. You could do something
like this to build an N tuple by calling a function N many times.
---
import std.typecons;
int foo() {
return 3;
}
auto initTuple(size_t N, alias func)() {
string magic() {
string result = return tuple(;
foreach(i; 0..N) {
result ~= func(),;
}
result ~= );;
return result;
}
mixin(magic());
}
void main(string[] argv) {
enum Tuple!(int, int, int) tup = initTuple!(3, foo);
}
---
This just builds the tuple by building up a mixin string which
calls the function so many times, with no guarantees about the
order of arguments. If you have side-effects in your function
though, you probably want to move it runtime anyway and use a
range with the 'repeat' function, etc.
Re: Getting a class' name, but not fully qualified?
You could do the following.
class Klass {
static class SubKlass {
}
}
string baseName(ClassInfo classinfo) {
import std.array;
import std.algorithm : countUntil;
import std.range : retro;
string qualName = classinfo.name;
size_t dotIndex = qualName.retro.countUntil('.');
if (dotIndex 0) {
return qualName;
}
return qualName[$ - dotIndex .. $];
}
string classBaseName(Object instance) {
if (instance is null) {
return null;
}
return instance.classinfo.baseName;
}
void main(string[] argv) {
import std.stdio;
writeln(Klass.classinfo.baseName);
writeln(Klass.SubKlass.classinfo.baseName);
Object x = new Klass();
Object y = new Klass.SubKlass();
writeln(x.classBaseName);
writeln(y.classBaseName);
}
The above won't result in any extra allocation and there are two
functions so you could find a class name both at compile time and
a runtime without too much trouble.
Re: Getting a class' name, but not fully qualified?
On Friday, 28 March 2014 at 20:47:39 UTC, JR wrote:
On Friday, 28 March 2014 at 13:42:43 UTC, w0rp wrote:
size_t dotIndex = qualName.retro.countUntil('.');
if (dotIndex 0) {
size_t is unsigned. :3
(So ptrdiff_t -- or simply auto.)
Oh yes, that is a bug. There's always at least one bug in an
example.
Re: enum VS static immutable
On Thursday, 13 March 2014 at 14:38:27 UTC, ref2401 wrote:
Hi.
I have this structure:
struct MyStruct {
enum MyStruct VALUE = MyStruct(5f);
static immutable MyStruct value = MyStruct(5f);
float data;
this(float v) { data = v; }
}
What's the difference between MyStruct.VALUE and
MyStruct.value? How should I decide what to use?
enum is a compile-time constant. 'static immutable' is an
immutable (and therefore implicitly shared between threads...)
runtime constant that isn't part of the struct itself. I'd stick
with enum and switch to static when what you're writing becomes
impossible to express at compile-time. A surprising number of
things can actually be expressed at compile-time.
Re: Does string.isNumeric mean that parse!int will not throw?
On Thursday, 20 February 2014 at 19:23:28 UTC, Cooler wrote:
On Thursday, 20 February 2014 at 19:18:15 UTC, Stanislav Blinov
wrote:
On Thursday, 20 February 2014 at 19:11:55 UTC, Cooler wrote:
The code:
string s = ...;
if(s.isNumeric){
auto x = parse!int(s); // Can I be sure here that parse will
not throw?
}
No. s may still contain data that is not convertible to int.
For
example, nan.
Is there any way to know that a string is convertible to a
number
without throwing?
You could do this.
import std.stdio;
import std.algorithm: all;
import std.ascii: isDigit;
void main(string[] args) {
writeln(123.all!isDigit); // true
writeln(12x.all!isDigit); // false
}
Combine the all algorithm which returns true if everything in a
range matches a predicate and use isDigit as the predicate
which returns true if the character is an ascii digit.
if (s.length 0 s.all!isDigit) {
// Never throws now.
auto x = parse!int(s);
}
Re: Does string.isNumeric mean that parse!int will not throw?
On Thursday, 20 February 2014 at 19:58:10 UTC, Stanislav Blinov
wrote:
On Thursday, 20 February 2014 at 19:46:35 UTC, w0rp wrote:
if (s.length 0 s.all!isDigit) {
// Never throws now.
auto x = parse!int(s);
}
And what about +/- and U/L suffixes? Or, say, different base
(i.e. hexadecimal)?
It would be way more beneficial if Phobos' parse (or some
additional function) returned some kind of Optional. Maybe a D
implementation of Andrei's ExpectedT?
True, this doesn't cover those. Returning a
Maybe/Option/Nullable/Whatever type from another function may be
better.
Re: C++ library says to delete data that it allocates
On Sunday, 22 September 2013 at 23:09:52 UTC, Charles Hixson wrote: I'm trying to use a C++ library that allocates data and returns a pointer to it. It tells me that I should delete the data when I'm through with it. Can I do this from within D? Or do I need to write some C++ code to manage the delete, and pass the pointer on to it? You can't use delete straight from D, so I'd write the delete in C++ and pass the pointer back to C++, like you say.
Re: Can call static method with null reference
You are invoking a function effectively stored statically in a class namespace. So you never actually dereference the null reference. You're just calling a function that doesn't really have anything to do with the reference. I prefer to tell it like it is and call the static method with the class name, so in this case that would be Foo.test1.
Re: Static member inside a class.
On Thursday, 13 June 2013 at 19:47:23 UTC, Agustin wrote:
I would like to know if static members are shared between 2
library. For example:
Class A
{
static uint var;
}
From Library A:
A::var = 3;
From Library B:
if( A::var == 3 )
...
Its this possible? if not, its any way to make it happend?
The members are shared between different modules, yes. You use .
instead of :: for scope resolution. You can also initialise a few
things in a static constructors at class scope...
class A {
static uint var;
static this() {
var = 3;
}
}
Or at module scope...
class A {
static uint var;
}
static this() {
A.var = 3;
}
You should note that the data isn't shared between threads by
default, but that's another detail. You can also usually produce
a design that uses non-static data instead of static data.
Re: opEquals does not work?
On Friday, 7 June 2013 at 20:51:13 UTC, Namespace wrote:
I got it. I must use Object instead of A... How ridiculous. I
thought this was already fixed...
The class opEquals is quite like .equals in Java. You need to
match the signature of Object, which is implicitly the base class
of all classes. I think I recommend something like this.
override bool opEquals(Object o) const {
auto other = cast(A) o;
// It's probably easy to miss out !is null here, which
matters.
return other !is null this.id == other.id;
}
Re: opEquals does not work?
On Friday, 7 June 2013 at 21:02:15 UTC, Namespace wrote: Yes, I remember. As I heard it the first time I thought it's because of the limited compiler and that it will fixed some day. opEquals for classes is interesting because you actually do need to write 'Object' there because of type polymorphism.
Re: opEquals does not work?
On Friday, 7 June 2013 at 21:18:12 UTC, Jonathan M Davis wrote: I have an open pull request as part of the move to getting rid of opEquals, opCmp, toHash, and toString from Object, and it would make it so that you could use something other than Object Oh, that's cool. I didn't know about that.
