support for firstindex (#494)

Author: fredrikekre

README.md

@@ -272,6 +272,8 @@ Currently, the `@compat` macro supports the following syntaxes:
 
 * `Dates.Period` rounding (e.g., `round(Dates.Hour(36), Dates.Day, RoundNearestTiesUp) == Dates.Day(2)` ([#24182]).
 
+* `firstindex` to obtain the first index of an iterable ([#25458]).
+
 
 ## Renaming
 

src/Compat.jl

@@ -1552,6 +1552,14 @@ end
 @static if !isdefined(Base, :lastindex)
     const lastindex = endof
     export lastindex
+    firstindex(a::AbstractArray) = (Base.@_inline_meta; first(linearindices(a)))
+    firstindex(c::Char) = 1
+    firstindex(c::Number) = 1
+    firstindex(p::Pair) = 1
+    firstindex(cmd::Cmd) = firstindex(cmd.exec)
+    firstindex(s::AbstractString) = 1
+    firstindex(t::Tuple) = 1
+    export firstindex
 end
 
 # 0.7.0-DEV.3585

test/runtests.jl

@@ -1330,6 +1330,7 @@ end
 # 0.7.0-DEV.3583
 @test lastindex(zeros(4)) == 4
 @test lastindex(zeros(4,4)) == 16
+@test all(x -> firstindex(x) == 1, ([1, 2], [1 2; 3 4], 'a', 1, 1=>2, `foo`, "foo", (1, 2)))
 
 # 0.7.0-DEV.3585
 let buf = IOBuffer()