Add equalto (#405)

README.md

@@ -172,6 +172,8 @@ Currently, the `@compat` macro supports the following syntaxes:
   `cov(::AbstractVector; corrected=)` and `cov(::AbstractVector, ::AbstractVector; corrected=)`
   are only available on 0.6. ([#21709])
 
+* `equalto` constructs an `EqualTo` object that can be used as a predicate ([#23812]).
+
 ## Renaming
 
 
@@ -331,3 +333,4 @@ includes this fix. Find the minimum version from there.
 [#23427]: https://github.com/JuliaLang/julia/issues/23427
 [#23570]: https://github.com/JuliaLang/julia/issues/23570
 [#23666]: https://github.com/JuliaLang/julia/issues/23666
+[#23812]: https://github.com/JuliaLang/julia/issues/23812

src/Compat.jl

@@ -663,6 +663,28 @@ end
     export isconcrete
 end
 
+# 0.7.0-DEV.1993
+@static if !isdefined(Base, :EqualTo)
+    if VERSION >= v"0.6.0"
+        include_string(@__MODULE__, """
+            struct EqualTo{T} <: Function
+                x::T
+
+                EqualTo(x::T) where {T} = new{T}(x)
+            end
+        """)
+    else
+        include_string(@__MODULE__, """
+            immutable EqualTo{T} <: Function
+                x::T
+            end
+        """)
+    end
+    (f::EqualTo)(y) = isequal(f.x, y)
+    const equalto = EqualTo
+    export equalto
+end
+
 include("deprecated.jl")
 
 end # module Compat

test/runtests.jl

@@ -823,6 +823,17 @@ end
 # 0.7
 @test isconcrete(Int)
 
+# 0.7
+let a = [0,1,2,3,0,1,2,3]
+    @test findfirst(equalto(3), [1,2,4,1,2,3,4]) == 6
+    @test findfirst(!equalto(1), [1,2,4,1,2,3,4]) == 2
+    @test findnext(equalto(1), a, 4) == 6
+    @test findnext(equalto(5), a, 4) == 0
+    @test findlast(equalto(3), [1,2,4,1,2,3,4]) == 6
+    @test findprev(equalto(1), a, 4) == 2
+    @test findprev(equalto(1), a, 8) == 6
+end
+
 if VERSION < v"0.6.0"
     include("deprecated.jl")
 end