Home » Community » U++ community news and announcements » Writable references to ValueArray/ValueMap/Value elements
| Writable references to ValueArray/ValueMap/Value elements [message #43612] |
Sat, 13 September 2014 16:31 |
 |
mirek
Messages: 13975
Registered: November 2005
|
Ultimate Member |
|
|
Lately I have found myself doing a lot of work on hierarchical Values (usually representing some JSON). Here, the strict non-mutable value-only features of Value make things a little bit complicated. Thus, after a long period of hesitation, I have introduced possibility to get a reference to "internal" Value contained in ValueArray/ValueMap/Value. It is now possible to write
Value v;
for(int i = 0; i < 3; i++) {
Value& p = v.At(i)("person");
p("name") = "Name" + AsString(i + 1);
p("lastname") = "LastName" + AsString(i + 1);
}
LOG(AsJSON(v));
and result is
[{"person":{"name":"Name1","lastname":"LastName1"}},{"person":{"name":"Name2","lastname":"LastName2"}},{"person":{"name":"Name3","lastname":"LastName3"}}]
However, there is a strict rule limiting the validity of such reference (caused by general nature of Value):
They are only valid until the next operation on originating Value - including just reading it!
Examples of faulty code:
Value m;
Value& x = m("key");
x = m; // using m as source invalidates x
Value m;
Value& x = m("key");
Value& y = m("key2"); // Invalidates x
x = 123; // undefined
Value m;
Value& x = m.At(1);
Value m2 = m; // Invalidates x
x = "fail"; // undefined
Mirek
|
|
|
|
Goto Forum:
Current Time: Fri Apr 19 05:00:01 CEST 2024
Total time taken to generate the page: 0.05016 seconds
|
Members
Pages
Help
Register
Login
Home
