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Low overhead, protected views over Java collections

There is a newer version: 1.2.3

package dev.marksman.collectionviews;

import com.jnape.palatable.lambda.adt.Maybe;
import com.jnape.palatable.lambda.functions.Fn0;

import java.util.Arrays;
import java.util.Objects;

import static com.jnape.palatable.lambda.adt.Maybe.just;
import static com.jnape.palatable.lambda.adt.Maybe.nothing;

class Sets {

    static  ImmutableSet empty() {
        return EmptySet.emptySet();
    }

    static  Maybe> maybeNonEmptyWrap(java.util.Set underlying) {
        Objects.requireNonNull(underlying);
        if (underlying.isEmpty()) {
            return nothing();
        } else {
            return just(new WrappedSet<>(underlying));
        }
    }

    static  Maybe> maybeNonEmptyWrap(Set underlying) {
        if (underlying instanceof NonEmptySet) {
            return just((NonEmptySet) underlying);
        } else if (!underlying.isEmpty()) {
            return just(new NonEmptySetAdapter<>(underlying));
        } else {
            return nothing();
        }
    }

    static Fn0 nonEmptyError() {
        return () -> new IllegalArgumentException("Cannot construct NonEmptySet from empty input");
    }

    @SuppressWarnings("varargs")
    @SafeVarargs
    static  ImmutableNonEmptySet nonEmptySetOf(A first, A... more) {
        java.util.Set underlying = new java.util.HashSet<>();
        underlying.add(first);
        underlying.addAll(Arrays.asList(more));
        return new ImmutableWrappedSet<>(underlying);
    }

    static  NonEmptySet nonEmptyWrapOrThrow(java.util.Set underlying) {
        return getNonEmptyOrThrow(maybeNonEmptyWrap(underlying));
    }

    static  NonEmptySet nonEmptyWrapOrThrow(Set underlying) {
        return getNonEmptyOrThrow(maybeNonEmptyWrap(underlying));
    }

    static  Set wrap(java.util.Set underlying) {
        Objects.requireNonNull(underlying);
        if (underlying.isEmpty()) {
            return empty();
        } else {
            return new WrappedSet<>(underlying);
        }
    }

    private static  NonEmptySet getNonEmptyOrThrow(Maybe> maybeResult) {
        return maybeResult.orElseThrow(nonEmptyError());
    }

}

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