YAML 中的单个感叹号有什么作用?

What does a single exclamation mark do in YAML?(YAML 中的单个感叹号有什么作用?)

问题描述

我正在使用 YamlDotNet 库，但在加载 YAML 文件时出现此错误:

<块引用>

解析标签时，未找到预期的标签 URI.

YAML 文件应该格式正确，因为它来自 就在 RoR.错误似乎是由这段代码触发的:

格式:默认: ！'%d-%m-%Y'长: ！%d %B, %Y"短的: ！'％D b'

我不是专家，但我从 YAML 规范中看到，您可以使用感叹号表示自定义对象/类型，使用两个感叹号表示明确的内置类型.

obj1: !custom # 不管obj2: !!str "我的字符串"

但是，我无法找到对上述使用的感叹号的任何引用.这是什么意思，为什么我使用的 YAML 库似乎无法解析它?请注意，如果我删除了这些感叹号，则该文件被解析得很好.

那个!是非特定标签.

YAML 规范 1.2(以及之前的 1.1) 说:

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通过明确指定！"非特定标签属性，节点然后将被解析为香草"序列、映射或字符串，各从其类.

查看这里标签语法":

<块引用>

none :未指定的标签(由应用程序自动解析).'！': 非特定标签(默认情况下，!!map"/!!seq"/!!str").'!foo' :主要的(按照惯例，表示本地的！foo"标签).'!!foo' :次要的(按照惯例，表示tag:yaml.org,2002:foo").'!h!foo': 需要 "%TAG !h!<前缀>"(然后表示<prefix>foo").'!':逐字标记(始终表示foo").

为什么 YamlDotNet 会抛出错误?我不能 100% 确定，但我认为你发现了一个错误.

YamlDotNet 是 LibYAML 的端口，因此很容易比较来源.

scanner.c (LibYAML) 的第 2635 行:

/* 检查标签是否为非空.*/如果(！长度){

Scanner.cs (YamlDotNet) 的第 2146 行:

//检查标签是否为非空.if (tag.Length == 0)

我知道，两者看起来非常相似，但此时 length 为 1，tag.Length 为 0.原始 C 代码负责初始的！"(全长)但 C# 不这样做(只是标签名称"长度).

向项目提交问题.

I'm working with the YamlDotNet library and I'm getting this error when loading a YAML file:

While parsing a tag, did not find expected tag URI.

The YAML file is supposed to be well-formed because it comes right from RoR. The error seems to be triggered by this code:

formats:
  default: ! '%d-%m-%Y'
  long: ! '%d %B, %Y'
  short: ! '%d %b'

I'm not an expert, but I see from the YAML spec that you can use an exclamation mark to indicate a custom object/type, and two exclamation marks to indicate an explicit built-in type.

obj1: !custom # whatever
obj2: !!str "My string"

However I haven't been able to find any reference to an exclamation mark used as above. What does that mean, and why the YAML library I use doesn't seem able to parse it? Note that if I remove those exclamation marks, the file is parsed fine.

That ! is the non-specific tag.

The YAML specification 1.2 (as well as the previous 1.1) says that :

By explicitly specifying a "!" non-specific tag property, the node would then be resolved to a "vanilla" sequence, mapping, or string, according to its kind.

Take a look here to the tag "grammar":

none    : Unspecified tag (automatically resolved by application).
'!'     : Non-specific tag (by default, "!!map"/"!!seq"/"!!str").
'!foo'  : Primary (by convention, means a local "!foo" tag).
'!!foo' : Secondary (by convention, means "tag:yaml.org,2002:foo").
'!h!foo': Requires "%TAG !h! <prefix>" (and then means "<prefix>foo").
'!<foo>': Verbatim tag (always means "foo").

Why is YamlDotNet throwing a error? I can't be 100% sure, but I think you found a bug.

YamlDotNet is a port of LibYAML, so it's easy to compare sources.

Line 2635 of scanner.c (LibYAML):

/* Check if the tag is non-empty. */
if (!length) {

Line 2146 of Scanner.cs (YamlDotNet ):

// Check if the tag is non-empty.
if (tag.Length == 0)

I know, both looks very similar, but at this point length is 1 and tag.Length is 0. Original C code takes care of the initial "!" (whole length) but C# doesn't do it (just the tag "name" length).

File an issue to the project.

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