Re: Can't add a const ubyte to a dynamic array of ubyte?

[a11e99z via Digitalmars-d-learn]

On Tuesday, 20 August 2019 at 09:49:21 UTC, Daniel Kozak wrote:
On Tue, Aug 20, 2019 at 11:30 AM ads via Digitalmars-d-learn 
 wrote:




you do not allow a person to think about a problem (and it’s easy 
here).
you carried him through a puddle now, but when he dives into Sea 
D, you will not be there :)

Re: Can't add a const ubyte to a dynamic array of ubyte?

[Jonathan M Davis via Digitalmars-d-learn]

On Tuesday, August 20, 2019 3:27:36 AM MDT ads via Digitalmars-d-learn 
wrote:
> import std.stdio;
>
> ubyte[] extend(in uint[] arr)
> {
>   ubyte[] result;
>   foreach (n; arr)
>   {
>   if (n < 10)
>   {
>   result ~= n;
>  // source/app.d(10,11): Error: cannot
> append type const(uint) to type ubyte[]
>   }
>   else
>   {
>   import std.conv : to;
>
>   foreach (digit; n.to!string)
>   {
>   result ~= digit.to!ubyte;
>   }
>   }
>   }
>   return result;
> }
>
> unittest
> {
>   import std.algorithm : equal;
>
>   assert(extend([1, 25, 70, 0]).equal([1, 2, 5, 7, 0, 0]));
> }
>
>
> How can I get around this? I want to ensure that the array is not
> mutated in the function in the signature too.

arr contains uints, not ubytes, so n is a uint, and you're trying to append
a uint to result, which is an array of ubytes. If you want to append n to
result, then you need to convert it to a ubyte - either by casting or by
using to!uint (the difference being that to will throw a ConvException if
the value of n doesn't fit in a ubyte). D does not allow implicit narrowing
conversions (because there's no guarantee that the value will fit in the
target type), so you can't assign a uint to a ubyte without an explicit
conversion - and that includes appending to an array of ubytes.

- Jonathan M Davis

Re: Can't add a const ubyte to a dynamic array of ubyte?

[a11e99z via Digitalmars-d-learn]

On Tuesday, 20 August 2019 at 09:27:36 UTC, ads wrote:

import std.stdio;

ubyte[] extend(in uint[] arr)
{
ubyte[] result;
foreach (n; arr)
{
if (n < 10)
result ~= n;
else
{
import std.conv : to;
foreach (digit; n.to!string)
result ~= digit.to!ubyte;
}
}
return result;
}

unittest
{
import std.algorithm : equal;
assert(extend([1, 25, 70, 0]).equal([1, 2, 5, 7, 0, 0]));
}

How can I get around this? I want to ensure that the array is 
not mutated in the function in the signature too.


what u using here?

result ~= digit.to!ubyte;

why not to do same in line?

result ~= n;


2) digit is '0'+(0..9) so u need subtract '0' ('0' is \x30)

Re: Can't add a const ubyte to a dynamic array of ubyte?

[Daniel Kozak via Digitalmars-d-learn]

On Tue, Aug 20, 2019 at 11:30 AM ads via Digitalmars-d-learn
 wrote:
>
>
> How can I get around this? I want to ensure that the array is not
> mutated in the function in the signature too.
>

https://run.dlang.io/is/tehp3j

import std.stdio;

ubyte[] extend(in uint[] arr)
{
ubyte[] result;
foreach (n; arr)
{
if (n < 10)
{
result ~= cast(ubyte)n;
// source/app.d(10,11): Error: cannot append type
const(uint) to type ubyte[]
}
else
{
import std.conv : to;

foreach (digit; n.to!string)
{
result ~= cast(ubyte)(digit - '0');
}
}
}
return result;
}

unittest
{
import std.algorithm : equal;
assert(extend([1, 25, 70, 0]).equal([1, 2, 5, 7, 0, 0]));
}

Can't add a const ubyte to a dynamic array of ubyte?

[ads via Digitalmars-d-learn]

import std.stdio;

ubyte[] extend(in uint[] arr)
{
ubyte[] result;
foreach (n; arr)
{
if (n < 10)
{
result ~= n;
// source/app.d(10,11): Error: cannot 
append type const(uint) to type ubyte[]

}
else
{
import std.conv : to;

foreach (digit; n.to!string)
{
result ~= digit.to!ubyte;
}
}
}
return result;
}

unittest
{
import std.algorithm : equal;

assert(extend([1, 25, 70, 0]).equal([1, 2, 5, 7, 0, 0]));
}


How can I get around this? I want to ensure that the array is not 
mutated in the function in the signature too.