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Add a variable to a class instance at runtime: Difference between revisions
Add a variable to a class instance at runtime (view source)
Revision as of 15:37, 31 August 2015
, 8 years agoadded Morfa
(Omit from Lily) |
(added Morfa) |
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Line 691:
Here, the two 'variables' can be seen under the single heading 'f'. And of course all of this is done at runtime.
=={{header|Morfa}}==
To emulate adding a variable to a class instance, Morfa uses user-defined operators <tt>`</tt> and <tt><-</tt>.
<lang morfa>
import morfa.base;
template <T>
public struct Dynamic
{
var data: Dict<text, T>;
}
// convenience to create new Dynamic instances
template <T>
public property dynamic(): Dynamic<T>
{
return Dynamic<T>(new Dict<text,T>());
}
// introduce replacement operator for . - a quoting ` operator
public operator ` { kind = infix, precedence = max, associativity = left, quoting = right }
template <T>
public func `(d: Dynamic<T>, name: text): DynamicElementAccess<T>
{
return DynamicElementAccess<T>(d, name);
}
// to allow implicit cast from the wrapped instance of T (on access)
template <T>
public func convert(dea: DynamicElementAccess<T>): T
{
return dea.holder.data[dea.name];
}
// cannot overload assignment - introduce special assignment operator
public operator <- { kind = infix, precedence = assign }
template <T>
public func <-(access: DynamicElementAccess<T>, newEl: T): void
{
access.holder.data[access.name] = newEl;
}
func main(): void
{
var test = dynamic<int>;
test`a <- 10;
test`b <- 20;
test`a <- 30;
println(test`a, test`b);
}
// private helper structure
template <T>
struct DynamicElementAccess
{
var holder: Dynamic<T>;
var name: text;
import morfa.io.format.Formatter;
public func format(formatt: text, formatter: Formatter): text
{
return getFormatFunction(holder.data[name])(formatt, formatter);
}
}
</lang>
{{out}}
<pre>
30 20
</pre>
=={{header|Objective-C}}==
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