How to throw a specific Exception in Julia

Question

I am doing test driven development in Julia. The test expects a certain exception to be thrown. How do I throw the expected exception?

I'm looping through a string and counting the occurrence of specific letters. Any letter than 'A','C','G',or'T' should result in an exception

Running Julia version 1.2.0.

I have tried these alternatives:

• throw(DomainError())
• throw(DomainError)
• throw("DomainError")

I expected those to work based on this resource: https://scls.gitbooks.io/ljthw/content/_chapters/11-ex8.html

这是我要解决的问题的链接：https : //exercism.io/my/solutions/781af1c1f9e2448cac57c0707aced90f

（请注意：该链接可能对我的登录名是唯一的）

我的代码：

function count_nucleotides(strand::AbstractString)

    Counts = Dict()
    Counts['A'] = 0
    Counts['C'] = 0
    Counts['G'] = 0
    Counts['T'] = 0

    for ch in strand
        # println(ch)
        if ch=='A'
            Counts['A'] += 1
            # Counts['A'] = Counts['A'] + 1
        elseif ch=='C'
            Counts['C'] += 1
        elseif ch=='G'
            Counts['G'] += 1
        elseif ch=='T'
            Counts['T'] += 1
        else
            throw(DomainError())
        end
    end

    return Counts
end

考试：

@testset "strand with invalid nucleotides" begin
    @test_throws DomainError count_nucleotides("AGXXACT")
end

我的错误报告，请参阅以下行：Expected和Thrown。

strand with invalid nucleotides: Test Failed at /Users/username/Exercism/julia/nucleotide-count/runtests.jl:18
  Expression: count_nucleotides("AGXXACT")
    Expected: DomainError
      Thrown: MethodError
Stacktrace:
 [1] top-level scope at /Users/shane/Exercism/julia/nucleotide-count/runtests.jl:18
 [2] top-level scope at /Users/juliainstall/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.2/Test/src/Test.jl:1113
 [3] top-level scope at /Users/username/Exercism/julia/nucleotide-count/runtests.jl:18
Test Summary:                   | Fail  Total
strand with invalid nucleotides |    1      1
ERROR: LoadError: Some tests did not pass: 0 passed, 1 failed, 0 errored, 0 broken.

Answer 1

该MethodError到来自呼叫DomainError没有为这个异常类型的无参数的构造函数- 。从文档：

help?> DomainError

  DomainError(val)
  DomainError(val, msg)

  The argument val to a function or constructor is outside the valid domain.

因此，有一个构造函数采用域外的值，另外一个构造函数采用额外的消息字符串。你可以做

throw(DomainError(ch))

要么

throw(DomainError(ch, "this character is bad"))