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Raise informative error for float/integer exponentiation that yields … #12822

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Aug 30, 2015
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Raise informative error for float/integer exponentiation that yields … #12822

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23 changes: 13 additions & 10 deletions base/replutil.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -106,11 +106,14 @@ function showerror(io::IO, ex::DomainError, bt; backtrace=true)
code = ccall(:jl_lookup_code_address, Any, (Ptr{Void}, Cint), b-1, true)
if length(code) == 5 && !code[4] # code[4] == fromC
if code[1] in (:log, :log2, :log10, :sqrt) # TODO add :besselj, :besseli, :bessely, :besselk
println(io,"\n$(code[1]) will only return a complex result if called with a complex argument.")
print(io, "try $(code[1]) (complex(x))")
elseif (code[1] == :^ && code[2] == symbol("intfuncs.jl")) || code[1] == :power_by_squaring
println(io, "\nCannot raise an integer x to a negative power -n. Make x a float by adding")
print(io, "a zero decimal (e.g. 2.0^-n instead of 2^-n), or write 1/x^n, float(x)^-n, or (x//1)^-n")
println(io,"\n$(code[1]) will only return a complex result if called with a complex argument. ",
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Hmm, this probably should have been print, not println; you added an extra newline to the output.

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@stevengj , actually that was the original design. I didn't introduce it. In fact, I'm not getting extraneous newlines comparing the output before and after your commit removing those println (e3d2cb7). Since I didn't notice that behavior, I didn't bother to change the old code.

Before

 _/ |\__'_|_|_|\__'_|  |  Commit 732860a (0 days old master)
|__/                   |  x86_64-apple-darwin14.5.0

julia> log(-2)
ERROR: DomainError:
log will only return a complex result if called with a complex argument.
try log (complex(x))
 in log at math.jl:139

julia> (-2.0)^(2.2)
ERROR: DomainError:
 in ^ at math.jl:275

After

 _/ |\__'_|_|_|\__'_|  |  Commit e3d2cb7 (0 days old master)
|__/                   |  x86_64-apple-darwin14.5.0

julia> log(-2)
ERROR: DomainError:
log will only return a complex result if called with a complex argument. Try log (complex(x)).
 in log at math.jl:139

julia> (-2.0)^(2.2)
ERROR: DomainError:
Exponentiation yielding a complex result requires a complex argument.
Replace x^y with (x+0im)^y, Complex(x)^y, or similar.
 in ^ at math.jl:275

"Try $(code[1]) (complex(x)).")
elseif (code[1] == :^ && code[2] == symbol("intfuncs.jl")) || code[1] == :power_by_squaring #3024
println(io, "\nCannot raise an integer x to a negative power -n. \nMake x a float by adding ",
"a zero decimal (e.g. 2.0^-n instead of 2^-n), or write 1/x^n, float(x)^-n, or (x//1)^-n.")
elseif code[1] == :^ && (code[2] == symbol("promotion.jl") || code[2] == symbol("math.jl"))
println(io, "\nExponentiation yielding a complex result requires a complex argument. ",
"\nReplace x^y with (x+0im)^y, Complex(x)^y, or similar.")
end
break
end
Expand Down Expand Up @@ -173,9 +176,9 @@ function showerror(io::IO, ex::MethodError)
push!(vec_args, isrow ? vec(arg) : arg)
end
if hasrows && applicable(f, vec_args...)
print(io, "\n\nYou might have used a 2d row vector where a 1d column vector was required.")
print(io, "\nNote the difference between 1d column vector [1,2,3] and 2d row vector [1 2 3].")
print(io, "\nYou can convert to a column vector with the vec() function.")
print(io, "\n\nYou might have used a 2d row vector where a 1d column vector was required.",
"\nNote the difference between 1d column vector [1,2,3] and 2d row vector [1 2 3].",
"\nYou can convert to a column vector with the vec() function.")
end
end
# Give a helpful error message if the user likely called a type constructor
Expand All @@ -185,8 +188,8 @@ function showerror(io::IO, ex::MethodError)
arg_types_param[1].name === Type.name)
construct_type = arg_types_param[1].parameters[1]
println(io)
print(io, "This may have arisen from a call to the constructor $construct_type(...),")
print(io, "\nsince type constructors fall back to convert methods.")
print(io, "This may have arisen from a call to the constructor $construct_type(...),",
"\nsince type constructors fall back to convert methods.")
end
show_method_candidates(io, ex)
end
Expand Down
5 changes: 5 additions & 0 deletions test/math.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -542,3 +542,8 @@ for f in binary_math_functions
@test f(x,[y]) == v
@test f([x],[y]) == v
end

# #3024, #12822
@test_throws DomainError 2 ^ -2
@test_throws DomainError (-2)^(2.2)
@test_throws DomainError (-2.0)^(2.2)