Deprecate Euler number e in favor of ℯ (U+212F)

This reduces confusion with variables called e, and ℯ is
the Unicode character for "natural exponent". It also
makes this constant more similar to others, which have
both a "special letter" and longer ASCII form.

Cf. #10607

base/constants.jl

@@ -99,33 +99,33 @@ big(x::MathConst) = convert(BigFloat,x)
 ## specific mathematical constants
 
 @math_const π        3.14159265358979323846  pi
-@math_const e        2.71828182845904523536  exp(big(1))
+@math_const ℯ        2.71828182845904523536  exp(big(1))
 @math_const γ        0.57721566490153286061  euler
 @math_const catalan  0.91596559417721901505  catalan
 @math_const φ        1.61803398874989484820  (1+sqrt(big(5)))/2
 
 # aliases
 const pi = π
-const eu = e
+const eu = ℯ
 const eulergamma = γ
 const golden = φ
 
 # special behaviors
 
-# use exp for e^x or e.^x, as in
-#    ^(::MathConst{:e}, x::Number) = exp(x)
-#    .^(::MathConst{:e}, x) = exp(x)
+# use exp for ℯ^x or ℯ.^x, as in
+#    ^(::MathConst{:ℯ}, x::Number) = exp(x)
+#    .^(::MathConst{:ℯ}, x) = exp(x)
 # but need to loop over types to prevent ambiguity with generic rules for ^(::Number, x) etc.
 for T in (MathConst, Rational, Integer, Number)
-    ^(::MathConst{:e}, x::T) = exp(x)
+    ^(::MathConst{:ℯ}, x::T) = exp(x)
 end
 for T in (Range, BitArray, SparseMatrixCSC, StridedArray, AbstractArray)
-    .^(::MathConst{:e}, x::T) = exp(x)
+    .^(::MathConst{:ℯ}, x::T) = exp(x)
 end
-^(::MathConst{:e}, x::AbstractMatrix) = expm(x)
+^(::MathConst{:ℯ}, x::AbstractMatrix) = expm(x)
 
-log(::MathConst{:e}) = 1 # use 1 to correctly promote expressions like log(x)/log(e)
-log(::MathConst{:e}, x) = log(x)
+log(::MathConst{:ℯ}) = 1 # use 1 to correctly promote expressions like log(x)/log(ℯ)
+log(::MathConst{:ℯ}, x) = log(x)
 
 #Align along = for nice Array printing
 function alignment(x::MathConst)

base/deprecated.jl

@@ -522,3 +522,44 @@ export float32_isvalid, float64_isvalid
 @deprecate parseint(s,base)           parse(Int, s, base)
 @deprecate parseint(T::Type, s)       parse(T, s)
 @deprecate parseint(T::Type, s, base) parse(T, s, base)
+
+# Deprecation of e MathConst
+export e
+const e = MathConst{:e}()
+
+e_depwarn() = depwarn("e mathematical constant is deprecated, use ℯ (\\u212F) or eu instead", :e)
+
+<(::MathConst{:e}, y::Rational{BigInt}) = (e_depwarn(); <(ℯ, y))
+<(x::Rational{BigInt}, ::MathConst{:e}) = (e_depwarn(); <(x, ℯ))
+<(::MathConst{:e}, y::Rational) = (e_depwarn(); <(ℯ, y))
+<(x::Rational, ::MathConst{:e}) =(e_depwarn();  <(x, ℯ))
+
+<(x::MathConst{:e}, y::Rational{BigInt}) = (e_depwarn(); <(ℯ, y))
+<(x::Rational{BigInt}, y::MathConst{:e}) = (e_depwarn(); <(x, ℯ))
+
+<=(x::MathConst{:e}, y::Rational) = (e_depwarn(); <=(ℯ, y))
+<=(x::Rational, y::MathConst{:e}) = (e_depwarn(); <=(x, ℯ))
+
+hash(x::MathConst{:e}, h::UInt) = (e_depwarn(); hash(ℯ, h))
+
+-(x::MathConst{:e}) = (e_depwarn(); -ℯ)
+for op in Symbol[:+, :-, :*, :/, :^]
+    @eval $op(x::MathConst{:e}, y::MathConst{:e}) = (e_depwarn(); $op(ℯ, ℯ))
+end
+
+convert(::Type{BigFloat}, ::MathConst{:e}) = (e_depwarn(); convert(BigFloat, ℯ))
+convert(::Type{Float64}, ::MathConst{:e}) = (e_depwarn(); convert(Float64, ℯ))
+convert(::Type{Float32}, ::MathConst{:e}) = (e_depwarn(); convert(Float32, ℯ))
+
+big(x::MathConst{:e}) = (e_depwarn(); big(ℯ))
+
+for T in (MathConst, Rational, Integer, Number)
+    ^(::MathConst{:e}, x::T) = (e_depwarn(); ^(ℯ, x))
+end
+for T in (Range, BitArray, SparseMatrixCSC, StridedArray, AbstractArray)
+    .^(::MathConst{:e}, x::T) = (e_depwarn(); .^(ℯ, x))
+end
+^(::MathConst{:e}, x::AbstractMatrix) = (e_depwarn(); ^(ℯ, x))
+
+log(::MathConst{:e}) = (e_depwarn(); log(ℯ))
+log(::MathConst{:e}, x) = (e_depwarn(); log(ℯ, x))

base/exports.jl

@@ -184,7 +184,7 @@ export
     NaN32,
     im,
     π, pi,
-    e, eu,
+    ℯ, eu,
     γ, eulergamma,
     catalan,
     φ, golden,

test/numbers.jl

@@ -2320,7 +2320,7 @@ end
 @test bswap(reinterpret(Float32,0x0000c03f)) === 1.5f0
 
 #isreal(x::Real) = true
-for x in [1.23, 7, e, 4//5] #[FP, Int, MathConst, Rat]
+for x in [1.23, 7, ℯ, 4//5] #[FP, Int, MathConst, Rat]
     @test isreal(x) == true
 end
 
@@ -2335,20 +2335,20 @@ for x in [subtypes(Complex); subtypes(Real)]
 end
 
 #getindex(x::Number) = x
-for x in [1.23, 7, e, 4//5] #[FP, Int, MathConst, Rat]
+for x in [1.23, 7, ℯ, 4//5] #[FP, Int, MathConst, Rat]
     @test getindex(x) == x
 end
 
 #copysign(x::Real, y::Real) = ifelse(signbit(x)!=signbit(y), -x, x)
 #same sign
-for x in [1.23, 7, e, 4//5]
-    for y in [1.23, 7, e, 4//5]
+for x in [1.23, 7, ℯ, 4//5]
+    for y in [1.23, 7, ℯ, 4//5]
         @test copysign(x,y) == x
     end
 end
 #different sign
-for x in [1.23, 7, e, 4//5]
-    for y in [1.23, 7, e, 4//5]
+for x in [1.23, 7, ℯ, 4//5]
+    for y in [1.23, 7, ℯ, 4//5]
         @test copysign(x, -y) == -x
     end
 end
@@ -2361,7 +2361,7 @@ end
 #in(x::Number, y::Number) = x == y
 @test in(3,3) == true #Int
 @test in(2.0,2.0) == true #FP
-@test in(e,e) == true #Const
+@test in(ℯ,ℯ) == true #Const
 @test in(4//5,4//5) == true #Rat
 @test in(1+2im, 1+2im) == true #Imag
 @test in(3, 3.0) == true #mixed