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Improve xsbti.Maybe 

* Make Nothing a singleton
* Make Maybe's constructor private
* Optimise equals to use reference equality first
* Optimise Just.equals by having proper, non-anonymous subclasses
* Having non-anonymous subclasses makes them have nicer classnames
* Give Just a value() method
This commit is contained in:
Dale Wijnand 2016-10-31 15:11:00 +00:00
parent ea56f331a1
commit 41c7e9b85d
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1 changed files with 38 additions and 39 deletions
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51
internal/util-interface/src/main/java/xsbti/Maybe.java
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@ -4,43 +4,42 @@
package xsbti; package xsbti;
/** Intended as a lightweight carrier for scala.Option. */ /** Intended as a lightweight carrier for scala.Option. */
public abstract class Maybe<t> public abstract class Maybe<t> {
{ private Maybe() {}
// private pending Scala bug #3642
protected Maybe() {} @SuppressWarnings("unchecked")
public static <s> Maybe<s> nothing() { return (Maybe<s>) Nothing.INSTANCE; }
public static <s> Maybe<s> just(final s v) { return new Just<s>(v); }
public static final class Just<s> extends Maybe<s> {
private final s v;
public Just(final s v) { this.v = v; }
public s value() { return v; }
public static <s> Maybe<s> just(final s v)
{
return new Maybe<s>() {
public boolean isDefined() { return true; } public boolean isDefined() { return true; }
public s get() { return v; } public s get() { return v; }
public int hashCode() { return 17 + (v == null ? 0 : v.hashCode()); } public int hashCode() { return 17 + (v == null ? 0 : v.hashCode()); }
public String toString() { return "Maybe.just(" + v + ")"; } public String toString() { return "Maybe.just(" + v + ")"; }
public boolean equals(Object o) { public boolean equals(Object o) {
if (o == null) return false; if (this == o) return true;
if (!(o instanceof Maybe)) return false; if (o == null || !(o instanceof Just<?>)) return false;
Maybe<?> other = (Maybe<?>) o; final Just<?> that = (Just<?>) o;
if (!other.isDefined()) return false; return v == null ? that.v == null : v.equals(that.v);
if (v == null) return other.get() == null;
return v.equals(other.get());
} }
};
} }
public static <s> Maybe<s> nothing()
{ public static final class Nothing extends Maybe<Object> {
return new Maybe<s>() { public static final Nothing INSTANCE = new Nothing();
private Nothing() { }
public boolean isDefined() { return false; } public boolean isDefined() { return false; }
public s get() { throw new UnsupportedOperationException("nothing.get"); } public Object get() { throw new UnsupportedOperationException("nothing.get"); }
public int hashCode() { return 1; } public int hashCode() { return 1; }
public String toString() { return "Maybe.nothing()"; } public String toString() { return "Maybe.nothing()"; }
public boolean equals(Object o) { public boolean equals(Object o) { return this == o || o != null && o instanceof Nothing; }
if (o == null) return false;
if (!(o instanceof Maybe)) return false;
Maybe<?> other = (Maybe<?>) o;
return !other.isDefined();
}
};
} }
public final boolean isEmpty() { return !isDefined(); } public final boolean isEmpty() { return !isDefined(); }