return this;
        }
    }

    class FixedExecutionTimeValue<T> extends ExecutionTimeValue<T> {
        private final T value;
        private final boolean changingContent;
        private final SideEffect<? super T> sideEffect;

        private FixedExecutionTimeValue(T value, boolean changingContent, @Nullable SideEffect<? super T> sideEffect) {
            this.value = value;

            return Optional.of(new FixedExecutionTimeValue(displayName, files));
        }

        private static class FixedExecutionTimeValue implements FileCollectionExecutionTimeValue {
            private final String displayName;
            private final ImmutableSet<File> files;

            public FixedExecutionTimeValue(String displayName, ImmutableSet<File> files) {