org.organicdesign.fp.oneOf.OneOf3 Maven / Gradle / Ivy
package org.organicdesign.fp.oneOf;
import org.organicdesign.fp.collections.ImList;
import org.organicdesign.fp.function.Fn1;
import org.organicdesign.fp.type.RuntimeTypes;
import java.util.Objects;
import static org.organicdesign.fp.type.RuntimeTypes.union2Str;
/**
Holds one of 3 values. See {@link OneOf2} for a full description. If you're passing the same type, you probably
want a tuple instead.
*/
public class OneOf3 {
private final Object item;
private final int sel;
private final ImList types;
/**
Protected constructor for subclassing.
@param o the item (may be null)
@param aClass class 0 (to have at runtime for descriptive error messages and toString()).
@param bClass class 1 (to have at runtime for descriptive error messages and toString()).
@param cClass class 2 (to have at runtime for descriptive error messages and toString()).
@param index 0 means this represents an A, 1 represents a B, 2 represents a C, 3 means D
*/
protected OneOf3(Object o, Class aClass, Class bClass, Class cClass, int index) {
types = RuntimeTypes.registerClasses(aClass, bClass, cClass);
sel = index;
item = o;
if (index < 0) {
throw new IllegalArgumentException("Selected item index must be 0-2");
} else if (index > 2) {
throw new IllegalArgumentException("Selected item index must be 0-2");
}
if ( (o != null) && (!types.get(index).isInstance(o)) ) {
throw new ClassCastException("You specified index " + index + ", indicating a(n) " +
types.get(index).getCanonicalName() + "," +
" but passed a " + o.getClass().getCanonicalName());
}
}
/**
Languages that have union types built in have a match statement that works like this method.
Exactly one of these functions will be executed - determined by which type of item this object holds.
@param fa the function to be executed if this OneOf stores the first type.
@param fb the function to be executed if this OneOf stores the second type.
@param fc the function to be executed if this OneOf stores the third type.
@return the return value of whichever function is executed.
*/
// We only store one item and it's type is erased, so we have to cast it at runtime.
// If sel is managed correctly, it ensures that the cast is accurate.
@SuppressWarnings("unchecked")
public R match(Fn1 fa,
Fn1 fb,
Fn1 fc) {
if (sel == 0) {
return fa.apply((A) item);
} else if (sel == 1) {
return fb.apply((B) item);
} else {
return fc.apply((C) item);
}
}
public int hashCode() {
// Simplest way to make the two items different.
return Objects.hashCode(item) + sel;
}
@SuppressWarnings("unchecked")
@Override public boolean equals(Object other) {
if (this == other) { return true; }
if (!(other instanceof OneOf3)) { return false; }
OneOf3 that = (OneOf3) other;
return (sel == that.sel) &&
Objects.equals(item, that.item);
}
@Override public String toString() { return union2Str(item, types); }
}