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UXEvaluable

UXEvaluable is the one-method protocol that makes a type filterable by UXPredicate.

#use <UXKit>            // or #import "UXPredicate.xc"

Overview

Section titled “Overview”
protocol UXEvaluable {
    u8* valueForKey(u8* key);
}

Implement this method and any predicate works on your type. The predicate does not need to know what your type is, and you do not write a filter method per query.

class File : Object <UXEvaluable> {
    u8* name; u8* kind; u8* size;


    u8* valueForKey(u8* key) {
        if (UXPredicate.streq(key, (u8*)"name")) { return name; }
        if (UXPredicate.streq(key, (u8*)"kind")) { return kind; }
        if (UXPredicate.streq(key, (u8*)"size")) { return size; }
        return (u8*)"";
    }
}
UXPredicate* p = UXPredicate.and(UXPredicate.equals((u8*)"kind", (u8*)"Source"),
                                 UXPredicate.contains_((u8*)"name", (u8*)"UX"));
p.evaluate((UXEvaluable*)file);

Topics

Section titled “Topics”

valueForKey

valueForKey

Section titled “valueForKey”
u8* valueForKey(u8* key)

The value for a key path, as a string.

Return "" (or 0) for a key you do not have. An absent key counts as empty, not as an error. A rule naming a field this object lacks fails to match instead of aborting a whole filter pass, so one rule editor can run over a heterogeneous list.

Everything is a string, and the operator decides how to read it. Numeric comparisons (< > <= >=) parse both sides as integers; = and != compare as strings. Under >, a size of "14" is greater than "9", where a string comparison would say otherwise. "512 B" reads as 512, because the parse takes the leading integer and units are not modelled.

You can keep values in whatever textual form your model already has, but unit suffixes are ignored, not interpreted.

Keeping it cheap

Section titled “Keeping it cheap”

valueForKey is called once per key per object per evaluation, so a filter over a large list calls it many times. Returning a stored field is ideal. If a key needs computing, consider holding the value in the model instead of computing it here.

See also

Section titled “See also”