Reduce code duplication in find* functions (JuliaLang#36965)

base/array.jl

@@ -1923,18 +1923,7 @@ julia> findnext(A, CartesianIndex(1, 1))
 CartesianIndex(2, 1)
 ```
 """
-function findnext(A, start)
- l = last(keys(A))
- i = oftype(l, start)
- i > l && return nothing
- while true
- A[i] && return i
- i == l && break
- # nextind(A, l) can throw/overflow
- i = nextind(A, i)
- end
- return nothing
-end
+findnext(A, start) = findnext(identity, A, start)
 
 """
  findfirst(A)
@@ -1971,14 +1960,7 @@ julia> findfirst(A)
 CartesianIndex(2, 1)
 ```
 """
-function findfirst(A)
- for (i, a) in pairs(A)
- if a
- return i
- end
- end
- return nothing
-end
+findfirst(A) = findfirst(identity, A)
 
 # Needed for bootstrap, and allows defining only an optimized findnext method
 findfirst(A::AbstractArray) = findnext(A, first(keys(A)))
@@ -2114,18 +2096,7 @@ julia> findprev(A, CartesianIndex(2, 1))
 CartesianIndex(2, 1)
 ```
 """
-function findprev(A, start)
- f = first(keys(A))
- i = oftype(f, start)
- i < f && return nothing
- while true
- A[i] && return i
- i == f && break
- # prevind(A, f) can throw/underflow
- i = prevind(A, i)
- end
- return nothing
-end
+findprev(A, start) = findprev(identity, A, start)
 
 """
  findlast(A)
@@ -2163,14 +2134,7 @@ julia> findlast(A)
 CartesianIndex(2, 1)
 ```
 """
-function findlast(A)
- for (i, a) in Iterators.reverse(pairs(A))
- if a
- return i
- end
- end
- return nothing
-end
+findlast(A) = findlast(identity, A)
 
 # Needed for bootstrap, and allows defining only an optimized findprev method
 findlast(A::AbstractArray) = findprev(A, last(keys(A)))
@@ -2360,9 +2324,8 @@ julia> findall(falses(3))
 Int64[]
 ```
 """
-function findall(A)
- collect(first(p) for p in pairs(A) if last(p))
-end
+findall(A) = findall(identity, A)
+
 # Allocating result upfront is faster (possible only when collection can be iterated twice)
 function findall(A::AbstractArray{Bool})
  n = count(A)