std.jgrandson

[Andrei Alexandrescu via Digitalmars-d]

On 8/4/14, 12:47 AM, Andrea Fontana wrote:
> On my bson library I found very useful to have some methods to know if a
> field exists or not, and to get a "defaulted" value. Something like:
>
> auto assume(T)(Value v, T default = T.init);

Nice. Probably "get" would be better to be in keep with built-in hashtables.

> Another good method could be something like xpath to get a deep value:
>
> Value v = value["/path/to/sub/object"];

Cool. Is it unlikely that a value contains an actual slash? If so would 
be value["path"]["to"]["sub"]["object"] more precise?

> Moreover in my library I actually have three different methods to read a
> value:
>
> T get(T)() // Exception if value is not a T or not valid or value
> doesn't exist
> T to(T)()  // Try to convert value to T using to!string. Exception if
> doesn't exists or not valid
>
> BsonField!T as(T)(lazy T default = T.init)  // Always return a value
>
> BsonField!T is an "alias this"-ed struct with two fields: T value and
> bool error(). T value is the aliased field, and error() tells you if
> value is defaulted (because of an error: field not exists or can't
> convert to T)
>
> So I can write something like this:
>
> int myvalue = json["/that/deep/property"].as!int;
>
> or
>
> auto myvalue = json["/that/deep/property"].as!int(10);
>
> if (myvalue.error) writeln("Property doesn't exists, I'm using default
> value);
>
> writeln("Property value: ", myvalue);
>
> I hope this can be useful...

Sure is, thanks. Listen, would you want to volunteer a std.data.json 
proposal?


Andrei