digitalmars.D.learn - Trying to use a template class with ranges
- mark (32/32) Feb 06 2020 I am starting on porting Python's difflib's sequence matcher to D.
- mark (7/7) Feb 06 2020 I forgot to mention: I want the class to work with:
- Steven Schveighoffer (24/64) Feb 06 2020 1. If one template parameter depends 100% on the other, it doesn't need
- mark (60/69) Feb 06 2020 On Thursday, 6 February 2020 at 15:21:46 UTC, Steven
- Steven Schveighoffer (3/5) Feb 06 2020 Hah, forgot that it's a class. Yes, I DID mean new Diff ;)
- mark (12/17) Feb 06 2020 Wow, that's all it needed to compile!
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); }
Feb 06 2020
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
Feb 06 2020
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
Feb 06 2020
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.
Feb 06 2020
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
Feb 06 2020
On Thursday, 6 February 2020 at 16:29:57 UTC, Steven Schveighoffer wrote:On 2/6/20 11:05 AM, mark wrote: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!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
Feb 06 2020