如何通过变量指定位串的类型

发布于 2024-08-17 23:51:56 字数 319 浏览 6 评论 0原文

Erlang 不允许我这样做：

Type = bitstring. 
<<FirstPart:8/Type, Rest/bitstring>> = some_binary.

尽管它允许我这样做：

Size = 8. 
<<FirstPart:Size/bitstring, Rest/bitstring>> = some_binary.

因此，在位字符串表达式中，虽然我可以通过变量传递大小，但它不允许我通过变量传递类型。有什么解决办法吗？

原文

Erlang doesn't let me do:

Type = bitstring. 
<<FirstPart:8/Type, Rest/bitstring>> = some_binary.

although it lets me do:

Size = 8. 
<<FirstPart:Size/bitstring, Rest/bitstring>> = some_binary.

So, in bit string expressions, while I can pass the size through a variable, It doesnt let me pass the type through a variable. Is there any solution?

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蛮可爱 2024-08-24 23:51:56

您可以使用 case 语句作为解决方法：

{FirstPart, Rest} = case Type of
                        {'bitstring', Len} ->
                            <<A:Len/bitstring, B/bitstring>> = Bin,
                            {A,B};
                        'integer' ->
                            <<A/integer, B/bitstring>> = Bin,
                            {A,B};
                        ...

You can use a case statement as a workaround:

{FirstPart, Rest} = case Type of
                        {'bitstring', Len} ->
                            <<A:Len/bitstring, B/bitstring>> = Bin,
                            {A,B};
                        'integer' ->
                            <<A/integer, B/bitstring>> = Bin,
                            {A,B};
                        ...

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浅笑依然 2024-08-24 23:51:56

我在这里没有看到任何特殊之处，使得条件处理不同“类型”的编码变得不方便。

case StringType of
  byte_len ->
    <<Len:8, String:Len/binary>> = SomeBinary,
    String;
  word_len ->
    <<Len:32, String:Len/binary>> = SomeBinary,
    String;
  etc -> ...
end

I do not see anything extraordinary here that makes a conditional inconvenient for handling the different "types" of encoding.

case StringType of
  byte_len ->
    <<Len:8, String:Len/binary>> = SomeBinary,
    String;
  word_len ->
    <<Len:32, String:Len/binary>> = SomeBinary,
    String;
  etc -> ...
end

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