Re: Trying to use a template class with ranges
On Thursday, 6 February 2020 at 16:29:57 UTC, Steven
Schveighoffer wrote:
On 2/6/20 11:05 AM, mark wrote:
src/package.d(50,35): Error: no property opCall for type
diffrange.Diff!(dchar[]), did you mean new Diff!(dchar[])?
Hah, forgot that it's a class. Yes, I DID mean new Diff ;)
-Steve
Wow, that's all it needed to compile!
And I've added the extra check you suggested:
auto differ(T)(T a, T b) if (
isForwardRange!T && // T is a range
is(typeof(T.init.front == T.init.front)) // Elements
support ==
) {
return new Diff!T(a, b);
}
Thanks!
Re: Trying to use a template class with ranges
On 2/6/20 11:05 AM, mark wrote: src/package.d(50,35): Error: no property opCall for type diffrange.Diff!(dchar[]), did you mean new Diff!(dchar[])? Hah, forgot that it's a class. Yes, I DID mean new Diff ;) -Steve
Re: Trying to use a template class with ranges
On Thursday, 6 February 2020 at 15:21:46 UTC, Steven
Schveighoffer wrote:
[snip]
3. You should declare constraints signifying what types are
valid. i.e.:
class Diff(T) if (
isForwardRange!T // it's a forward range
&& is(typeof(T.init.front == T.init.front)) // elements are
comparable
)
Might be good to put this constraint on the factory function
too.
I don't know how to do that syntactically. I tried the obvious
and it wouldn't compile.
But even without that it won't compile although it is much closer
now!
import std.range: ElementType, front, isForwardRange;
class Diff(T) if (
isForwardRange!T && // T is a range
is(typeof(T.init.front == T.init.front)) // Elements
support ==
) {
alias E = ElementType!T;
T a;
T b;
size_t[][E] b2j;
this(T a, T b) {
this.a = a;
this.b = b;
chainB();
}
private final void chainB() {
foreach (i, element; b)
b2j[element] ~= i;
// TODO
}
}
auto differ(T)(T a, T b) { return Diff!T(a, b); }
unittest {
import std.array;
import std.stdio: writeln;
writeln("unittest for the diffrange library.");
auto d1 = differ("one two three four".array, "one too tree
four".array);
auto a = ["Tulips are yellow,", "Violets are blue,", "Agar is
sweet,",
"As are you."];
auto b = ["Roses are red,", "Violets are blue,", "Sugar is
sweet,",
"And so are you."];
auto d2 = differ(a, b);
}
Here's the error output:
Excluding package.d file from test due to
https://issues.dlang.org/show_bug.cgi?id=11847
src/package.d(50,35): Error: no property opCall for type
diffrange.Diff!(dchar[]), did you mean new Diff!(dchar[])?
src/package.d(57,21): Error: template instance
diffrange.differ!(dchar[]) error instantiating
src/package.d(50,35): Error: no property opCall for type
diffrange.Diff!(string[]), did you mean new Diff!(string[])?
src/package.d(62,21): Error: template instance
diffrange.differ!(string[]) error instantiating
/home/mark/opt/bin/ldc2 failed with exit code 1.
Curiously the "Excluding package.d file" message isn't true.
Not that I mind, I just want to be able to get it going.
Thanks!
PS The line numbers don't match because I've deleted some structs
& enums that are above the class but which aren't used yet.
Re: Trying to use a template class with ranges
On 2/6/20 7:16 AM, mark wrote:
I am starting on porting Python's difflib's sequence matcher to D.
I want to have a class that will accept two ranges whose elements are of
the same type and whose elements can be compared for equality.
How do I make a class declaration that specifies a (forward) range type
and an equality-supporting element type?
Here's what doesn't work:
class Diff(T, E) {
T a; // T should be a forward range of E elements
T b; // E elements must support == and !=
// This is a hash key=E element, value=slice of size_t
size_t[][E] b2j;
this(T a, T b) {
this.a = a;
this.b = b;
chainB();
}
void chainB() {
foreach (i, element; b)
b2j[element] ~= i;
// TODO
}
}
unittest {
import std.stdio: writeln;
writeln("unittest for the diffrange library.");
auto a = ["Tulips are yellow,", "Violets are blue,",
"Agar is sweet,", "As are you."];
auto b = ["Roses are red,", "Violets are blue,",
"Sugar is sweet,", "And so are you."];
auto diff = Diff(a, b);
}
1. If one template parameter depends 100% on the other, it doesn't need
to be a parameter. i.e. I would do:
class Diff(T) {
alias E = ElementType!T;
...
}
2. Class constructors do not support IFTI. You have to explicitly
instantiate. To use IFTI, you need to create a factory function. i.e. to
make the code above work, your ctor call should be Diff!(typeof(a))
(assuming you take the advice in 1).
But you can instead write a function to use IFTI:
auto makeDiff(T)(T r1, T r2) { return Diff!T(r1, r2); }
...
auto diff = makeDiff(a, b);
3. You should declare constraints signifying what types are valid. i.e.:
class Diff(T) if (
isForwardRange!T // it's a forward range
&& is(typeof(T.init.front == T.init.front)) // elements are comparable
)
Might be good to put this constraint on the factory function too.
Note: is(typeof(...)) basically checks if the thing inside the typeof
compiles.
-Steve
Re: Trying to use a template class with ranges
I forgot to mention: I want the class to work with: Diff(aForwardRange, bForwardRange) where T = ForwardRange, E = anything that supports == A common use case is for two sequences of strings (i.e., lines read from two files). Diff(aString, bString) where T = char[] or wchar[] or dchar[] E = char or wchar or dchar
Trying to use a template class with ranges
I am starting on porting Python's difflib's sequence matcher to D.
I want to have a class that will accept two ranges whose elements
are of the same type and whose elements can be compared for
equality.
How do I make a class declaration that specifies a (forward)
range type and an equality-supporting element type?
Here's what doesn't work:
class Diff(T, E) {
T a; // T should be a forward range of E elements
T b; // E elements must support == and !=
// This is a hash key=E element, value=slice of size_t
size_t[][E] b2j;
this(T a, T b) {
this.a = a;
this.b = b;
chainB();
}
void chainB() {
foreach (i, element; b)
b2j[element] ~= i;
// TODO
}
}
unittest {
import std.stdio: writeln;
writeln("unittest for the diffrange library.");
auto a = ["Tulips are yellow,", "Violets are blue,",
"Agar is sweet,", "As are you."];
auto b = ["Roses are red,", "Violets are blue,",
"Sugar is sweet,", "And so are you."];
auto diff = Diff(a, b);
}
