Re: help cast
On Monday, 19 March 2018 at 11:20:05 UTC, Steven Schveighoffer wrote: Let me adjust your example a bit, and see if you still agree: auto bytes = cast(ubyte[])[55_444, 289, 1_000_000, 846, 123_456_789]; writeln(bytes); // [148, 33, 64, 78, 21] I have used cast(ubyte[]) to get ubytes as well, but I normally would do this for values that actually *could be* ubytes. for values higher than ubytes, I would not have expected implicit truncation. It's especially confusing to someone who has seen when you cast an int[] to a ubyte[], and gets the bytes for that same data. When I use cast(ubyte[]), I took it to mean "pretend this is a ubyte[] literal", not "cast each element to ubyte". I can also see this biting someone who has a long set of ubytes, and accidentally does one that is larger than 255. -Steve Raw `cast` is just nasty. It's overloaded and confusing. Wrapper template functions like `reinterpretBitsAs` can help alleviate the pain, e.g. `assert([1, 2, 3].reinterpretBitsAs!(ubyte[]).length == 12);`. I feel like C++ got it right (or just less wrong) with casts.
Re: help cast
On Monday, 19 March 2018 at 11:20:05 UTC, Steven Schveighoffer wrote: On 3/18/18 4:07 PM, Jonathan M Davis wrote: That's exactly what it's doing, and when you have multiple elements in the literal, it quickly gets a lot more pleasant than casting each element individually. e.g. cast(ubyte[])[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10] vs [cast(ubyte)0, cast(ubyte)1, cast(ubyte)2, cast(ubyte)3, cast(ubyte)4, cast(ubyte)5, cast(ubyte)6, cast(ubyte)7, cast(ubyte)8, cast(ubyte)9, cast(ubyte)10] I use this trick all the time when creating arrays of integral types smaller than int, precisely because casting each element is a royal pain and way harder to read. Let me adjust your example a bit, and see if you still agree: auto bytes = cast(ubyte[])[55_444, 289, 1_000_000, 846, 123_456_789]; writeln(bytes); // [148, 33, 64, 78, 21] I have used cast(ubyte[]) to get ubytes as well, but I normally would do this for values that actually *could be* ubytes. for values higher than ubytes, I would not have expected implicit truncation. It's especially confusing to someone who has seen when you cast an int[] to a ubyte[], and gets the bytes for that same data. When I use cast(ubyte[]), I took it to mean "pretend this is a ubyte[] literal", not "cast each element to ubyte". I can also see this biting someone who has a long set of ubytes, and accidentally does one that is larger than 255. -Steve An even funnier example. auto bytes = cast(ubyte[])cast(int[])[55_444, 289, 1_000_000, 846, 123_456_789]; auto bytes2 = cast(int[])[55_444, 289, 1_000_000, 846, 123_456_789]; auto bytes3 = cast(ubyte[])bytes2; writeln(bytes); // Guess what the output is here. writeln(bytes2); // Prints:[55444, 289, 100, 846, 123456789] writeln(bytes3); // Prints: [148, 216, 0, 0, 33, 1, 0, 0, 64, 66, 15, 0, 78, 3, 0, 0, 21, 205, 91, 7]
Re: help cast
On 3/18/18 4:07 PM, Jonathan M Davis wrote: That's exactly what it's doing, and when you have multiple elements in the literal, it quickly gets a lot more pleasant than casting each element individually. e.g. cast(ubyte[])[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10] vs [cast(ubyte)0, cast(ubyte)1, cast(ubyte)2, cast(ubyte)3, cast(ubyte)4, cast(ubyte)5, cast(ubyte)6, cast(ubyte)7, cast(ubyte)8, cast(ubyte)9, cast(ubyte)10] I use this trick all the time when creating arrays of integral types smaller than int, precisely because casting each element is a royal pain and way harder to read. Let me adjust your example a bit, and see if you still agree: auto bytes = cast(ubyte[])[55_444, 289, 1_000_000, 846, 123_456_789]; writeln(bytes); // [148, 33, 64, 78, 21] I have used cast(ubyte[]) to get ubytes as well, but I normally would do this for values that actually *could be* ubytes. for values higher than ubytes, I would not have expected implicit truncation. It's especially confusing to someone who has seen when you cast an int[] to a ubyte[], and gets the bytes for that same data. When I use cast(ubyte[]), I took it to mean "pretend this is a ubyte[] literal", not "cast each element to ubyte". I can also see this biting someone who has a long set of ubytes, and accidentally does one that is larger than 255. -Steve
Re: help cast
On Sunday, 18 March 2018 at 20:07:28 UTC, Jonathan M Davis wrote:
On Sunday, March 18, 2018 14:56:04 Steven Schveighoffer via
Digitalmars-d wrote:
On 3/18/18 2:24 PM, Jonathan M Davis wrote:
> On Sunday, March 18, 2018 13:10:28 Steven Schveighoffer via
> Digitalmars-d
>
> wrote:
>> On 3/18/18 4:34 AM, sdvcn wrote:
>>> dchar v11=dchar.max;
>>>
>>> auto vp11 = [v11];
>>>
>>> auto v2 = cast(ubyte[]) (vp11); //v2.length=4
>>> auto v22 = cast(ubyte[])( [v11]); //v2.length=1
>>
>> This seems like a bug to me.
>>
>> It appears that v22 has truncated v11 to a byte and made
>> only a single byte array out of it.
>
> Except that that's precisely how you usually get an array
> any integral type smaller than an integer. e.g.
>
> auto arr = cast(ubyte[])([1, 2, 3, 4]);
>
> In this case, you could do
>
> ubyte[] arr = [1, 2, 3, 4];
>
> instead, but if you're not dealing with an initializaton or
> assignment like this (e.g. you're passing the array to a
> functon), then the cast is the way you do it. Normally, you
> do it with integer literals, and I could see an argument
> that it shouldn't allow it without VRP being used to make it
> work, but it _is_ a cast, and casts are a bit of a blunt
> instrument.
>
> So, I really don't think that it's a bug.
It's quite possible that you aren't understanding what is
happening:
ubyte[] arr = cast(ubyte[])[555];
writeln(arr); // [43]
Why is this not a bug? I didn't cast the 555 to a ubyte, so it
should either complain that it can't do it, or give me an
array of 4 bytes.
I guess it could be explained as the same thing as:
ubyte[] arr = [cast(ubyte)555];
But this is surprisingly weird behavior.
That's exactly what it's doing, and when you have multiple
elements in the literal, it quickly gets a lot more pleasant
than casting each element individually. e.g.
cast(ubyte[])[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
vs
[cast(ubyte)0, cast(ubyte)1, cast(ubyte)2, cast(ubyte)3,
cast(ubyte)4,
cast(ubyte)5, cast(ubyte)6, cast(ubyte)7, cast(ubyte)8,
cast(ubyte)9,
cast(ubyte)10]
I use this trick all the time when creating arrays of integral
types smaller than int, precisely because casting each element
is a royal pain and way harder to read.
- Jonathan M Davis
代码目的是转换任意类行到ubyte[]
The object of the code is to convert any class of rows to ubyte[]
但是非数组类无法正确转化
But non - array classes can't be converted correctly
void pByte(T)(T v)
{
ubyte[] uBuf;
static if(isArray!T){
uBuf = cast(ubyte[])mKey;
}else{
uBuf = cast(ubyte[])[v];
}
writeln(uBuf);
}
无法得到正确结果
Unable to get the correct result
Re: help cast
On Sunday, March 18, 2018 14:56:04 Steven Schveighoffer via Digitalmars-d wrote: > On 3/18/18 2:24 PM, Jonathan M Davis wrote: > > On Sunday, March 18, 2018 13:10:28 Steven Schveighoffer via > > Digitalmars-d > > > > wrote: > >> On 3/18/18 4:34 AM, sdvcn wrote: > >>> dchar v11=dchar.max; > >>> > >>> auto vp11 = [v11]; > >>> > >>> auto v2 = cast(ubyte[]) (vp11); //v2.length=4 > >>> auto v22 = cast(ubyte[])( [v11]); //v2.length=1 > >> > >> This seems like a bug to me. > >> > >> It appears that v22 has truncated v11 to a byte and made only a single > >> byte array out of it. > > > > Except that that's precisely how you usually get an array any integral > > type smaller than an integer. e.g. > > > > auto arr = cast(ubyte[])([1, 2, 3, 4]); > > > > In this case, you could do > > > > ubyte[] arr = [1, 2, 3, 4]; > > > > instead, but if you're not dealing with an initializaton or assignment > > like this (e.g. you're passing the array to a functon), then the cast > > is the way you do it. Normally, you do it with integer literals, and I > > could see an argument that it shouldn't allow it without VRP being used > > to make it work, but it _is_ a cast, and casts are a bit of a blunt > > instrument. > > > > So, I really don't think that it's a bug. > > It's quite possible that you aren't understanding what is happening: > > ubyte[] arr = cast(ubyte[])[555]; > writeln(arr); // [43] > > Why is this not a bug? I didn't cast the 555 to a ubyte, so it should > either complain that it can't do it, or give me an array of 4 bytes. > > I guess it could be explained as the same thing as: > > ubyte[] arr = [cast(ubyte)555]; > > But this is surprisingly weird behavior. That's exactly what it's doing, and when you have multiple elements in the literal, it quickly gets a lot more pleasant than casting each element individually. e.g. cast(ubyte[])[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10] vs [cast(ubyte)0, cast(ubyte)1, cast(ubyte)2, cast(ubyte)3, cast(ubyte)4, cast(ubyte)5, cast(ubyte)6, cast(ubyte)7, cast(ubyte)8, cast(ubyte)9, cast(ubyte)10] I use this trick all the time when creating arrays of integral types smaller than int, precisely because casting each element is a royal pain and way harder to read. - Jonathan M Davis
Re: help cast
On 3/18/18 2:24 PM, Jonathan M Davis wrote: On Sunday, March 18, 2018 13:10:28 Steven Schveighoffer via Digitalmars-d wrote: On 3/18/18 4:34 AM, sdvcn wrote: dchar v11=dchar.max; auto vp11 = [v11]; auto v2 = cast(ubyte[]) (vp11); //v2.length=4 auto v22 = cast(ubyte[])( [v11]); //v2.length=1 This seems like a bug to me. It appears that v22 has truncated v11 to a byte and made only a single byte array out of it. Except that that's precisely how you usually get an array any integral type smaller than an integer. e.g. auto arr = cast(ubyte[])([1, 2, 3, 4]); In this case, you could do ubyte[] arr = [1, 2, 3, 4]; instead, but if you're not dealing with an initializaton or assignment like this (e.g. you're passing the array to a functon), then the cast is the way you do it. Normally, you do it with integer literals, and I could see an argument that it shouldn't allow it without VRP being used to make it work, but it _is_ a cast, and casts are a bit of a blunt instrument. So, I really don't think that it's a bug. It's quite possible that you aren't understanding what is happening: ubyte[] arr = cast(ubyte[])[555]; writeln(arr); // [43] Why is this not a bug? I didn't cast the 555 to a ubyte, so it should either complain that it can't do it, or give me an array of 4 bytes. I guess it could be explained as the same thing as: ubyte[] arr = [cast(ubyte)555]; But this is surprisingly weird behavior. -Steve
Re: help cast
On Sunday, March 18, 2018 13:10:28 Steven Schveighoffer via Digitalmars-d wrote: > On 3/18/18 4:34 AM, sdvcn wrote: > > dchar v11=dchar.max; > > > > auto vp11 = [v11]; > > > > auto v2 = cast(ubyte[]) (vp11); //v2.length=4 > > auto v22 = cast(ubyte[])( [v11]); //v2.length=1 > > This seems like a bug to me. > > It appears that v22 has truncated v11 to a byte and made only a single > byte array out of it. Except that that's precisely how you usually get an array any integral type smaller than an integer. e.g. auto arr = cast(ubyte[])([1, 2, 3, 4]); In this case, you could do ubyte[] arr = [1, 2, 3, 4]; instead, but if you're not dealing with an initializaton or assignment like this (e.g. you're passing the array to a functon), then the cast is the way you do it. Normally, you do it with integer literals, and I could see an argument that it shouldn't allow it without VRP being used to make it work, but it _is_ a cast, and casts are a bit of a blunt instrument. So, I really don't think that it's a bug. - Jonathan M Davis
Re: help cast
On 3/18/18 4:34 AM, sdvcn wrote: dchar v11=dchar.max; auto vp11 = [v11]; auto v2 = cast(ubyte[]) (vp11); //v2.length=4 auto v22 = cast(ubyte[])( [v11]); //v2.length=1 This seems like a bug to me. It appears that v22 has truncated v11 to a byte and made only a single byte array out of it. -Steve
