Add a variable to a class instance at runtime: Difference between revisions

=={{header|Morfa}}==

To emulate adding a variable to a class instance, Morfa uses user-defined operators <tt>`</tt> and <tt>&lt;-</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>