Re: Can an alias be used to define a new anchor?

On Tue, Sep 9, 2014 at 9:27 PM, Bartek Grychtol <[email protected]> wrote:
> Hello List,
>
> I'm new to YAML, which we're using in a project via yaml-cpp. I stumpled
> into an issue which I don't know if it's a bug in yaml-cpp or a feature of
> the spec. I consulted the spec but left no wiser.
>
> I wanted to write a node like this:
> ---
> Images:
>  one:
>   size_x: &ONE_SIZE 100
>  two:
>   size_x: &TWO_SIZE *ONE_SIZE
>
> That is, I was hoping to use an alias to define a new anchor. The motivation
> is that *TWO_SIZE is used lower down independently of *ONE_SIZE, yet they
> are sometimes, but not always, one and the same thing.
>
> yaml-cpp refuses to parse this. Is it legal YAML?
>
> Thanks in advance!
>
> Bartek
>

Bartek,

I'm afraid it is not legal YAML. Once you assign an anchor name to a
node, you have to reuse that anchor name for all aliases.

The production for aliases is under section 7.1.

http://www.yaml.org/spec/1.2/spec.html#id2786196

[104] 	c-ns-alias-node 	::= 	“*” ns-anchor-name

[102] 	ns-anchor-char 	::= 	ns-char - c-flow-indicator 	
[103] 	ns-anchor-name 	::= 	ns-anchor-char+

In the current spec (1.2), there is no way of assigning multiple
anchor/alias names to the same node.

However, there may be future versions of the spec which don't have
this limitation.

Best regards,
Peter

-- 
Email: [email protected]
WWW: http://www.pkmurphy.com.au/

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