Vector {AbstractString}函数参数将不接受julia中的Vector {String}输入 [英] Vector{AbstractString} function parameter won't accept Vector{String} input in julia

问题描述

Julia中的以下代码:

The following code in Julia:

function foo(a::Vector{AbstractString})  
end
foo(["a"])

出现以下错误:

ERROR: MethodError: no method matching foo(::Array{String,1})
Closest candidates are:
  foo(::Array{AbstractString,1}) at REPL[77]:2

即使按预期运行了以下代码:

Even though the following code runs, as expected:

function foo(a::Vector{String})  
end
foo(["a"])

此外，AbstractString通常与String匹配，如下所示:

And further, AbstractString generally matches String as in:

function foo(::AbstractString)  
end
foo("a")

如果我有String个元素，如何使用Vector{AbstractString}参数调用函数?

How can I call a function with a Vector{AbstractString} parameter if I have String elements?

推荐答案

您需要这样编写函数签名:

You need to write the function signature like this:

function foo{S<:AbstractString}(a::Vector{S})
    # do stuff
end

在Julia 0.6及更高版本上，也可以改写

On Julia 0.6 and newer, it's also possible to write instead

function foo(a::Vector{<:AbstractString})
    # do stuff
end

这是Julia中参数类型不变的结果.请参见有关类型的章节有关详细信息，请参见手册.

This is a consequence of parametric type invariance in Julia. See the chapter on types in the manual for more details.

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