Add Char * String and Char * Char #22532

adamslc · 2017-06-25T16:46:38Z

Solves #22512. I am definitely a Github novice, so let me know if I made a stupid mistake somewhere...

KristofferC · 2017-06-25T16:53:30Z

Perhaps you could also add some tests of the kind 'a' * "b" * 'c' etc?

added extra tests

adamslc · 2017-06-25T17:32:13Z

I've added a few more tests. I tried to squash the extra commit, but I just made a horrible mess. How should I do that?

KristofferC · 2017-06-25T17:33:44Z

It's OK, it can be squashed on merge with the github ui.

pabloferz · 2017-06-25T20:06:44Z

base/strings/basic.jl

@@ -68,6 +68,9 @@ julia> "Hello " * "world"
 ```
 """
 (*)(s1::AbstractString, ss::AbstractString...) = string(s1, ss...)
+(*)(c::Char, s::AbstractString) = string(c, s)
+(*)(s::AbstractString, c::Char) = string(s, c)
+(*)(c1::Char, c2::Char) = string(c1, c2)


We might subsume all these with

(*)(s::AbstractString, ss::Union{Char,AbstractString}...) = string(s, ss...) (*)(c::Char, ss::Union{Char,AbstractString}...) = string(c, ss...)

and take advantage of the string(::Union{Char,String}...) method.

I reduced it further to one method (see next commit)

andyferris · 2017-06-25T23:20:58Z

~~I was wondering about concatenating characters to make this operation more complete, e.g. char * char and things like 'a' * 'b' * "c" vs "a" * 'b' * 'c'.~~

Sorry I misread :)

andyferris · 2017-06-25T23:21:02Z

PS ++ rules 😜

tkelman · 2017-06-26T01:37:10Z

docstring should be updated here - it isn't formatted correctly on master, signatures should be indented, not backtick fenced

tkelman · 2017-06-26T02:01:32Z

base/strings/basic.jl

-```
-*(s::AbstractString, t::AbstractString)
-```
+    *(s::Union{Char, AbstractString}, t::Union{Char, AbstractString})


... on the second input

adamslc · 2017-06-26T16:03:45Z

Does this need anything else?

pabloferz · 2017-06-26T16:12:40Z

There was a timeout on linux 32-bit so I restated the build (gist backed-up here https://gist.github.com/pabloferz/4cb263e0967ba9a5c3256bc53d3619ee)

fredrikekre · 2017-06-26T18:47:35Z

base/strings/basic.jl


-Concatenate strings. The `*` operator is an alias to this function.
+Concatenate strings and characters. The `*` operator is an alias to this function.


"[...] and characters to a [`String`](@ref)." perhaps?

Also, this is the * function, its an alias for itself!?

I would make it like this:

""" *(s::Union{AbstractString, Char}, t::Union{AbstractString, Char}) Concatenate strings and/or characters, producing a [`String`](@ref). This is equivalent to calling the [`string`](@ref) function on the arguments. """

tkelman · 2017-06-30T05:28:55Z

base/strings/basic.jl

+Concatenate strings and/or characters, producing a [`String`](@ref). This is equivalent
+to calling the [`string`](@ref) function on the arguments.
+
+# Examples



delete the blank line

I thought we had been putting lines between the headers and contents in docstring?

Ah, I guess not.

recently moving towards getting rid of them everywhere

K, thanks for the heads up

musm · 2017-06-30T06:29:25Z

base/strings/basic.jl

 ```
 """
-(*)(s1::AbstractString, ss::AbstractString...) = string(s1, ss...)
+(*)(s1::Union{Char, AbstractString}, ss::Union{Char, AbstractString}...) = string(s1, ss...)


Aside from some of the linalg code, typically there isn't a space after the comma in Union. Probably best to keep consistency within this file and alike.

StefanKarpinski · 2017-07-11T15:32:07Z

Unless there are objections, I plan to merge this in 24 hours.

pabloferz · 2017-07-11T15:37:11Z

base/strings/basic.jl

@@ -56,9 +56,12 @@ sizeof(s::AbstractString) = error("type $(typeof(s)) has no canonical binary rep
 eltype(::Type{<:AbstractString}) = Char

 """
-    *(s::Union{Char, AbstractString}, t::Union{Char, AbstractString}...)
+    *(s::Union{AbstractString, Char}, t::Union{AbstractString, Char})


Why where the three dots removed?

ararslan · 2017-07-11T18:17:52Z

Once the ... is added back to the docstring, LGTM.

KristofferC · 2017-07-11T18:39:37Z

Just add it back (with collaborator access to the branch) and merge?

[ci skip]

ararslan · 2017-07-11T18:46:20Z

Good idea, @KristofferC. Done.

ararslan · 2017-07-11T18:47:29Z

Thanks for the contribution, @adamslc! Nice work here.

[ci skip]

stevengj · 2017-07-12T01:14:48Z

Two problems:

Since it defines Char * Char = String, it should also define one(::Type{Char}) = "".
Should probably have a specialized Char^Integer method similar to the String^Integer method.

ararslan · 2017-07-12T01:16:59Z

Regarding one, isn't it typically assumed that one(::Type{T}) has type T? Defining that method for Char would break that, and AFAIK it would be the only exception. (There may be others that I don't know about though.)

stevengj · 2017-07-12T01:20:33Z

@ararslan, no, that is not correct. e.g. one for a dimensionful quantity returns a different type. (If you want the same type, you call oneunit, which isn't defined here.)

One the other hand, it is true that "" isn't really a multiplicative identity for Char, since "" * 'x' == "x", not 'x'. That makes me think we shouldn't define one after all.

stevengj · 2017-07-12T01:22:45Z

We should definitely have a specialized ^, however. The default one isn't type-stable for Char and is grossly inefficient for this type anyway.

musm · 2017-07-12T17:53:10Z

@stevengj

The following specialized version of repeat, which ^ calls, seems to work fine.

function repeat(s::Char, r::Integer)
    r < 0 && throw(ArgumentError("can't repeat a char $r times"))
    out = _string_n(r)
    ccall(:memset, Ptr{Void}, (Ptr{UInt8}, Cint, Csize_t), out, s, r)
    return out
end

There isn't much speed improvement over repeat(s::String,r::Integer)

stevengj · 2017-07-12T18:03:28Z

(That only works for isascii(s). For non-ascii I would just call string(s)^r as a fallback.)

musm · 2017-07-12T18:55:31Z

Calling repeat(string(s), 3) would allocate and makes it about twice as slow.

stevengj · 2017-07-12T19:12:19Z

@musm, I understand that, but since char^integer and string^integer are almost exclusively used for ASCII chars (mainly for repeating spaces), I think it is fine to optimize mainly the ASCII case of char^integer and leave the non-ASCII case to a slower fallback for now.

StefanKarpinski · 2017-07-12T19:39:32Z

To implement an efficient character repeating operator, it's sufficient to figure out what 1-4 byte pattern the character produces in UTF-8 and then copy that as many times as the character needs to be repeated. Not entirely straightforward, but not crazy to implement either.

ararslan · 2017-07-12T19:43:04Z

Is there something relevant already implemented in utf8proc?

stevengj · 2017-07-12T20:11:16Z

Stefan, I know its possible, but I don't think it is worth the trouble

StefanKarpinski · 2017-07-12T20:39:56Z

Sure, can always be done as an optimization in the future some time.

[ci skip]

…iaLang#22766)

musm · 2017-09-20T04:00:17Z

@ScottPJones sent me the following version which does not allocate a while back. I don't think he has had the time to open a PR on his branch so I am posting this here in the hopes that someone opens a PR with the change

function repeat(c::Char, r::Integer)
    r < 0 && throw(ArgumentError("can't repeat a character $r times"))
    r == 0 && return ""
    ch = UInt(c)
    if ch < 0x80
        out = Base._string_n(r)
        ccall(:memset, Ptr{Void}, (Ptr{UInt8}, Cint, Csize_t), out, c, r)
    elseif ch < 0x800
        out = _string_n(2r)
        p16 = reinterpret(Ptr{UInt16}, pointer(out))
        u16 = ((ch >> 0x6) | (ch & 0x3f) << 0x8) % UInt16 | 0x80c0
        @inbounds for i = 1:r
            unsafe_store!(p16, u16, i)
        end
    elseif ch < 0x10000
        (0xd800 ≥ ch ≤ 0xdfff) || throw(ArgumentError("invalid character 0x$(hex(ch))"))
        out = _string_n(3r)
        p = pointer(out)
        b1 = (ch >> 0xc) % UInt8 | 0xe0
        b2 = ((ch >> 0x6) & 0x3f) % UInt8 | 0x80
        b3 = (ch & 0x3f) % UInt8 | 0x80
        @inbounds for i = 1:r
            unsafe_store!(p, b1)
            unsafe_store!(p, b2, 2)
            unsafe_store!(p, b3, 3)
            p += 3
        end
    elseif ch < 0x110000
        out = _string_n(4r)
        p32 = reinterpret(Ptr{UInt32}, pointer(out))
        u32 = ((ch >> 0x12) | ((ch >> 0x4) & 0x03f00) |
            ((ch << 0xa) & 0x3f0000) | ((ch & 0x3f) << 0x18)) % UInt32 | 0x808080f0
        @inbounds for i = 1:r
            unsafe_store!(p32, u32)
            p32 += 4
        end
    else
        throw(ArgumentError("invalid character 0x$(hex(ch))"))
    end
    return out
end

StefanKarpinski · 2017-09-20T05:13:36Z

Thanks, PR: #23787.

added char concat methods

c20972c

kshyatt added the domain:strings "Strings!" label Jun 25, 2017

Luke Adams added 2 commits June 25, 2017 11:22

added char concat methods

c6dec74

added extra tests

added more tests

7ce7e1a

pabloferz reviewed Jun 25, 2017

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condense methods

7313f5d

update docstring

c377c83

tkelman reviewed Jun 26, 2017

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add ...

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KristofferC approved these changes Jun 26, 2017

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fredrikekre reviewed Jun 26, 2017

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Minor docstring improvement

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ararslan approved these changes Jun 30, 2017

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tkelman reviewed Jun 30, 2017

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ararslan added 2 commits June 29, 2017 22:34

Remove line

df56a8f

Merge branch 'master' into char_concat

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musm reviewed Jun 30, 2017

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pabloferz reviewed Jul 11, 2017

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Add back the ...

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[ci skip]

ararslan merged commit f98b857 into JuliaLang:master Jul 11, 2017

ararslan added a commit that referenced this pull request Jul 11, 2017

Add a NEWS entry for #22532: Char concatenation using *

8ee74a9

[ci skip]

musm mentioned this pull request Jul 12, 2017

Add specialized repeat function for Char #22785

Closed

ararslan added a commit that referenced this pull request Jul 15, 2017

Add a NEWS entry for #22532: Char concatenation using *

ee21d82

[ci skip]

ararslan added a commit that referenced this pull request Jul 15, 2017

Add a NEWS entry for #22532: Char concatenation using *

26ca36c

[ci skip]

ararslan added a commit that referenced this pull request Jul 15, 2017

Add a NEWS entry for #22532: Char concatenation using * (#22766)

0b2774e

jeffwong pushed a commit to jeffwong/julia that referenced this pull request Jul 24, 2017

Add Char * String and Char * Char (JuliaLang#22532)

8fcb668

jeffwong pushed a commit to jeffwong/julia that referenced this pull request Jul 24, 2017

Add a NEWS entry for JuliaLang#22532: Char concatenation using * (Jul…

7ac2d81

…iaLang#22766)


		Concatenate strings. The `*` operator is an alias to this function.
		Concatenate strings and characters. The `*` operator is an alias to this function.

Add Char * String and Char * Char #22532

Add Char * String and Char * Char #22532

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