Re: Question about: ("1.1").to!int;
On Wednesday, 21 October 2020 at 22:50:27 UTC, matheus wrote:
Hi,
import std.stdio, std.conv;
void main(string[ ] args) {
auto a = (1).to!int; // this works
auto b = ("1").to!int; // this works
auto c = (1.1).to!int; // this works and c = 1
auto d = ("1.1").to!int; // Doesn't work
}
The forth line gives me:
std.conv.ConvException@/usr/include/dlang/dmd/std/conv.d(1898):
Unexpected '.' when converting from type string to type int
??:? pure @safe int std.conv.toImpl!(int,
immutable(char)[]).toImpl(immutable(char)[]) [0x55de76d9b4d7]
??:? pure @safe int
std.conv.to!(int).to!(immutable(char)[]).to(immutable(char)[])
[0x55de76d99a17]
??:? _Dmain [0x55de76d9986e]
Question:
Since (1.1).to!int = 1, shouldn't the string value
("1.1").to!int at least try to convert to float/double and then
to int?
Because for what I see "to!int" converts from: int,real but in
case of string only when it is a integer representation?
Matheus.
In first case you asked to convert a float (inferred by templace
function) to int in the second case, you asked for the function
"convert this string contaning a set of digits to an int for me".
Doesn't make sense do something else than the asked. D has static
if() and a nice way to do type comparasion at compile time. It
does optimize things alot.
I haven't read the to source code, but consider it may use the
idea like this:
auto to(T, T2)(T2 source)
{
// you asked for int, doesn't makes sense consider a float
here.
// that would waste time checking for floats when you
programmer's requested
// was clear: an integer.
static if(is(T == int) && is(T2 == string))
{
int v = 0;
foreach(c; source)
v = v * 10 + c - '0';
return v;
}
// the string to float point conversion algorithm
static if(is(T == float) && is(T2 == string))
{
/* ... */
}
static if(is(T == int) && is(T2 == double))
{
return cast(int)source;
}
assert(0, "unknow type");
}
Re: Question about: ("1.1").to!int;
On Saturday, 24 October 2020 at 14:10:02 UTC, matheus wrote:
On Saturday, 24 October 2020 at 04:04:18 UTC, Виталий Фадеев
wrote:
On Friday, 23 October 2020 at 16:59:06 UTC, matheus wrote:
On Friday, 23 October 2020 at 13:57:41 UTC, Joseph Rushton
Wakeling wrote:
On Wednesday, 21 October 2020 at 22:50:27 UTC, matheus wrote:
I don't get...
(1.1).to!int = 1.
("1.1").to!int = Current is an error and IMO should be 1.
Matheus.
You should write converter from string to int.
Then you will understand.
You converter input:
"1"
"1.1"
"1.1.1"
"1a"
"1.1a"
"a"
".1"
".1.1"
You converter must be fast.
Re: Question about: ("1.1").to!int;
On Saturday, 24 October 2020 at 04:04:18 UTC, Виталий Фадеев
wrote:
On Friday, 23 October 2020 at 16:59:06 UTC, matheus wrote:
On Friday, 23 October 2020 at 13:57:41 UTC, Joseph Rushton
Wakeling wrote:
On Wednesday, 21 October 2020 at 22:50:27 UTC, matheus wrote:
Well since the caller is handling a string, shouldn't the
caller verify the content before any conversion?
What if:
"1.1.1".to!int
?
The algorithm will become more complicated?
Will the speed decrease?
I don't get...
Anyway this should fail, look "1.1" is one thing, "1.1.1" is
another thing as "1.a" is another thing.
Like I said before I think the behavior should be the same in
these cases:
(1.1).to!int = 1.
("1.1").to!int = Current is an error and IMO should be 1.
Now for your question:
1.1.1.to!int = Error: found `0.1` when expecting `,`.
"1.1.1".to!int = Should be the same as above.
Matheus.
Re: Question about: ("1.1").to!int;
On Friday, 23 October 2020 at 16:59:06 UTC, matheus wrote: On Friday, 23 October 2020 at 13:57:41 UTC, Joseph Rushton Wakeling wrote: On Wednesday, 21 October 2020 at 22:50:27 UTC, matheus wrote: Well since the caller is handling a string, shouldn't the caller verify the content before any conversion? What if: "1.1.1".to!int ? The algorithm will become more complicated? Will the speed decrease?
Re: Question about: ("1.1").to!int;
On Friday, 23 October 2020 at 16:59:06 UTC, matheus wrote:
On Friday, 23 October 2020 at 13:57:41 UTC, Joseph Rushton
Wakeling wrote:
On Wednesday, 21 October 2020 at 22:50:27 UTC, matheus wrote:
Since (1.1).to!int = 1, shouldn't the string value
("1.1").to!int at least try to convert to float/double and
then to int?
The thing is, that's a great way for hard-to-identify bugs to
creep into code. In these cases:
auto a = (1).to!int; // this works
auto b = ("1").to!int; // this works
auto c = (1.1).to!int; // this works and c = 1
... then what the programmer wants is unambiguous. In the
first case it's just converting int => int. In the second,
it's converting from a string that unambiguously represents an
integer value, to an int. And in the third, it's converting
_at programmer request_ from a double to an int (which has a
well-defined behaviour).
However, if ("1.1").to!int were to work, this would be the
`to` function making a judgement call on how to handle
something ambiguous. And while that judgement call may be
acceptable for your current use-case, it won't be for others.
I got it everything you said, but like a said previously:
(1.1).to!int vs ("1.1").to!int
One is a decimal literal while the other is a string
representation of a decimal.
To be honest I think the function is already making a judgment
call when I do (1.1).to!int and returns 1, I really fail to see
the difference when is ("1.1").to!int.
I agree with user1234: "The third case is just like `cast(int)
1.1` it's not _at programmer request_ from my point of view,
it's just that the `to` template has not be more restrictive
than the D `cast` expression. `to` should do at least what a
`cast` do and do more when there's no rule for the two types
that are involved."
In particular, if `to` just accepted any string numerical
representation for conversion to int, how could the caller
explicitly _exclude_ non-integer input, if that is their
use-case?
Well since the caller is handling a string, shouldn't the
caller verify the content before any conversion?
Because a string may contain a integer, decimal representation
or neither one.
Finally I don't want to make a fuss of it, I just thought it
was a bit weird but it can be solved easily.
Thanks,
Matheus.
For _execution speed_ reason we need low-level functions.
What if on each call ("1").to!int we will do parsing "1" for
decimal point "." ?
.
Should be Low-level functions and High-level functions.
"to" is Low-level function.
.
You can create "To" function with parsing & validating.
You right: if "to" generating exception for non-numeric symbol,
then it doing test each char... and "to" can just break loop at
non-numeric symbol.
.
And...
.
"1".to!int
"1.1".to!int
"1abc".to!int
...they all can be == 1
.
Some like this:
foreach( c; str )
if ( c.between( '0', '9' ) )
result *= factor; result += ( c-'0' );
else
break;
.
You can write patch.
Re: Question about: ("1.1").to!int;
On Friday, 23 October 2020 at 13:57:41 UTC, Joseph Rushton
Wakeling wrote:
On Wednesday, 21 October 2020 at 22:50:27 UTC, matheus wrote:
Since (1.1).to!int = 1, shouldn't the string value
("1.1").to!int at least try to convert to float/double and
then to int?
The thing is, that's a great way for hard-to-identify bugs to
creep into code. In these cases:
auto a = (1).to!int; // this works
auto b = ("1").to!int; // this works
auto c = (1.1).to!int; // this works and c = 1
... then what the programmer wants is unambiguous. In the
first case it's just converting int => int. In the second,
it's converting from a string that unambiguously represents an
integer value, to an int. And in the third, it's converting
_at programmer request_ from a double to an int (which has a
well-defined behaviour).
However, if ("1.1").to!int were to work, this would be the `to`
function making a judgement call on how to handle something
ambiguous. And while that judgement call may be acceptable for
your current use-case, it won't be for others.
I got it everything you said, but like a said previously:
(1.1).to!int vs ("1.1").to!int
One is a decimal literal while the other is a string
representation of a decimal.
To be honest I think the function is already making a judgment
call when I do (1.1).to!int and returns 1, I really fail to see
the difference when is ("1.1").to!int.
I agree with user1234: "The third case is just like `cast(int)
1.1` it's not _at programmer request_ from my point of view, it's
just that the `to` template has not be more restrictive than the
D `cast` expression. `to` should do at least what a `cast` do and
do more when there's no rule for the two types that are involved."
In particular, if `to` just accepted any string numerical
representation for conversion to int, how could the caller
explicitly _exclude_ non-integer input, if that is their
use-case?
Well since the caller is handling a string, shouldn't the caller
verify the content before any conversion?
Because a string may contain a integer, decimal representation or
neither one.
Finally I don't want to make a fuss of it, I just thought it was
a bit weird but it can be solved easily.
Thanks,
Matheus.
Re: Question about: ("1.1").to!int;
On Friday, 23 October 2020 at 14:16:50 UTC, user1234 wrote: The third case is just like `cast(int) 1.1` it's not _at programmer request_ from my point of view If the programmer explicitly writes a `to!int` or the `cast(int)`, then it's pretty clearly at their request. And it's unambiguous what they are asking for. But if the input to the conversion is a string, it's important that the conversion fail unless the string is an unambiguous representation of the intended destination type. Otherwise, there is more than one data conversion going on, and one of them is being hidden from the programmer.
Re: Question about: ("1.1").to!int;
On Friday, 23 October 2020 at 13:57:41 UTC, Joseph Rushton
Wakeling wrote:
In particular, if `to` just accepted any string numerical
representation for conversion to int, how could the caller
explicitly _exclude_ non-integer input, if that is their
use-case?
So it's far better to require you, as the programmer, to make
what you want unambiguous and explicitly write code that will
(i) deserialize any numerical string that is acceptable to you
and (ii) convert to integer.
Yes, that's the problem, and it doesn't make sense to use a
statically typed language if the standard library silently
introduces holes that lead to serious bugs (in this case, loss of
numerical precision, which can be pretty nasty).
The solution is simple in this case, and it even leads to one
less character when you're writing your program:
import std;
void main()
{
int toInt(string s) {
return(s.to!double.to!int);
}
writeln(toInt("1"));
writeln(toInt("1.1"));
writeln(toInt("a"));
}
Re: Question about: ("1.1").to!int;
On Friday, 23 October 2020 at 13:57:41 UTC, Joseph Rushton
Wakeling wrote:
On Wednesday, 21 October 2020 at 22:50:27 UTC, matheus wrote:
Since (1.1).to!int = 1, shouldn't the string value
("1.1").to!int at least try to convert to float/double and
then to int?
The thing is, that's a great way for hard-to-identify bugs to
creep into code. In these cases:
auto a = (1).to!int; // this works
auto b = ("1").to!int; // this works
auto c = (1.1).to!int; // this works and c = 1
... then what the programmer wants is unambiguous. In the
first case it's just converting int => int. In the second,
it's converting from a string that unambiguously represents an
integer value, to an int. And in the third, it's converting
_at programmer request_ from a double to an int (which has a
well-defined behaviour).
However, if ("1.1").to!int were to work, this would be the `to`
function making a judgement call on how to handle something
ambiguous. And while that judgement call may be acceptable for
your current use-case, it won't be for others.
In particular, if `to` just accepted any string numerical
representation for conversion to int, how could the caller
explicitly _exclude_ non-integer input, if that is their
use-case?
So it's far better to require you, as the programmer, to make
what you want unambiguous and explicitly write code that will
(i) deserialize any numerical string that is acceptable to you
and (ii) convert to integer.
The third case is just like `cast(int) 1.1` it's not _at
programmer request_ from my point of view, it's just that the
`to` template has not be more restrictive than the D `cast`
expression. `to` should do at least what a `cast` do and do more
when there's no rule for the two types that are involved.
Re: Question about: ("1.1").to!int;
On Wednesday, 21 October 2020 at 22:50:27 UTC, matheus wrote:
Since (1.1).to!int = 1, shouldn't the string value
("1.1").to!int at least try to convert to float/double and then
to int?
The thing is, that's a great way for hard-to-identify bugs to
creep into code. In these cases:
auto a = (1).to!int; // this works
auto b = ("1").to!int; // this works
auto c = (1.1).to!int; // this works and c = 1
... then what the programmer wants is unambiguous. In the first
case it's just converting int => int. In the second, it's
converting from a string that unambiguously represents an integer
value, to an int. And in the third, it's converting _at
programmer request_ from a double to an int (which has a
well-defined behaviour).
However, if ("1.1").to!int were to work, this would be the `to`
function making a judgement call on how to handle something
ambiguous. And while that judgement call may be acceptable for
your current use-case, it won't be for others.
In particular, if `to` just accepted any string numerical
representation for conversion to int, how could the caller
explicitly _exclude_ non-integer input, if that is their use-case?
So it's far better to require you, as the programmer, to make
what you want unambiguous and explicitly write code that will (i)
deserialize any numerical string that is acceptable to you and
(ii) convert to integer.
Re: Question about: ("1.1").to!int;
On Friday, 23 October 2020 at 08:09:13 UTC, Виталий Фадеев wrote:
On Wednesday, 21 October 2020 at 22:50:27 UTC, matheus wrote:
Hi,
import std.stdio, std.conv;
void main(string[ ] args) {
auto a = (1).to!int; // this works
auto b = ("1").to!int; // this works
auto c = (1.1).to!int; // this works and c = 1
auto d = ("1.1").to!int; // Doesn't work
}
[...]
1.1 is not int.
"to" works fine.
As solution,... "1.1" should be splitted to lexems: "1", ".",
"1". Then analyze and then converted to int.
Of course 1.1 it's not an integer, but since (1.1).to!int works I
thought that ("1.1").to!int should work too.
Matheus.
Re: Question about: ("1.1").to!int;
On Wednesday, 21 October 2020 at 22:50:27 UTC, matheus wrote:
Hi,
import std.stdio, std.conv;
void main(string[ ] args) {
auto a = (1).to!int; // this works
auto b = ("1").to!int; // this works
auto c = (1.1).to!int; // this works and c = 1
auto d = ("1.1").to!int; // Doesn't work
}
[...]
1.1 is not int.
"to" works fine.
As solution,... "1.1" should be splitted to lexems: "1", ".",
"1". Then analyze and then converted to int.
Re: Question about: ("1.1").to!int;
On Wednesday, 21 October 2020 at 22:50:27 UTC, matheus wrote:
Since (1.1).to!int = 1, shouldn't the string value
("1.1").to!int at least try to convert to float/double and then
to int?
I don't think so. A silent string->double conversion isn't IMO
consistent with D's design.
"1.1".to!double.to!int works fine, and I like that you have to be
explicit, because there is so much room for error.
Note that "1".to!double.to!int works as expected. Therefore you
should be able to use that all the time.
Question about: ("1.1").to!int;
Hi,
import std.stdio, std.conv;
void main(string[ ] args) {
auto a = (1).to!int; // this works
auto b = ("1").to!int; // this works
auto c = (1.1).to!int; // this works and c = 1
auto d = ("1.1").to!int; // Doesn't work
}
The forth line gives me:
std.conv.ConvException@/usr/include/dlang/dmd/std/conv.d(1898):
Unexpected '.' when converting from type string to type int
??:? pure @safe int std.conv.toImpl!(int,
immutable(char)[]).toImpl(immutable(char)[]) [0x55de76d9b4d7]
??:? pure @safe int
std.conv.to!(int).to!(immutable(char)[]).to(immutable(char)[])
[0x55de76d99a17]
??:? _Dmain [0x55de76d9986e]
Question:
Since (1.1).to!int = 1, shouldn't the string value ("1.1").to!int
at least try to convert to float/double and then to int?
Because for what I see "to!int" converts from: int,real but in
case of string only when it is a integer representation?
Matheus.
