Why doesn't rand work with AbstractFloat?

Question

In Julia 0.4.0, when I try

rand(AbstractFloat, 1)

The following error is obtained:

ERROR: MethodError: `rand` has no method matching rand(::MersenneTwister,
::Type{AbstractFloat})

Is there a reason behind the fact that I must explicitly say Float32 or Float64 for rand to work? Or is it just that, as the language is relatively new, a relevant method has yet to be defined in the Base?

Answer 1

one与rand不同。 使用one(AbstractFloat)时，所有输出都是＆＃34;相同＆＃34;：

julia> one(Float64)
1.0

julia> one(Float32)
1.0f0

julia> 1.0 == 1.0f0
true

使用rand时不是这样：

julia> rand(srand(1), Float64)
0.23603334566204692

julia> rand(srand(1), Float32)
0.5479944f0

julia> rand(srand(1), Float32) == rand(srand(1), Float64)
false

这意味着如果rand的行为类似one，则可能会在两台不同的计算机上使用相同的种子获得两个不同的结果（例如，一个是x86，另一个是x64）。看看random.jl中的代码：

  

@inline rand {T＆lt;：Union {Bool，Int8，UInt8，Int16，UInt16，Int32，UInt32}}（r :: MersenneTwister，:: Type {T}）= rand_ui52_raw（r）％T

rand(Signed)＆amp; rand(Unsigned)也是非法的。