问题
The YAML spec clearly states:
Mappings use a colon and space (“: ”) to mark each key: value pair.
So this is legal:
foo: bar
But this, Ain't:
foo:bar
I see many people online that are ranting about the space. I think they have a point. I got burned by it several times myself.
Why is the space mandatory? What was the design consideration behind it?
回答1:
It's easy to miss, because that specification uses the bizarre convention of only highlighting the last character of an internal link, but the “: ” in the section you quote is actually a link to another section of the specification which answers your question:
Normally, YAML insists the “:” mapping value indicator be separated from the value by white space. A benefit of this restriction is that the “:” character can be used inside plain scalars, as long as it is not followed by white space. This allows for unquoted URLs and timestamps. It is also a potential source for confusion as “a:1” is a plain scalar and not a key: value pair.
So the motivation is that you can write lists such as this without requiring any quoting:
useful_values:
- 2:30
- http://example.com
- localhost:8080
If the space was optional, this could end up being ambiguous, and interpreted as a set of key-value pairs.
Aside: Here's a snippet of JS to make the link formatting on that document less useless.
document.styleSheets[0].insertRule('a[href^="#"] { color: #00A !important; text-decoration: underline !important; background: none !important; }', 0);
来源：https://stackoverflow.com/questions/42124227/why-does-the-yaml-spec-mandate-a-space-after-the-colon