def transformer = Mock(Transformer)
        def property = propertyWithNoValue()

        when:
        def provider = property.map(transformer)

        then:
        0 * _

        when:
        property.set(someValue())
        def r1 = provider.get()

        then:
        r1 == someOtherValue()
        1 * transformer.transform(someValue()) >> someOtherValue()

	// in this case, leading whitespace
	revertTransformer := store.UpdatePrefixTransformer(
		func(transformer *PrefixTransformer) value.Transformer {
			transformer.prefix = []byte(string(transformer.prefix) + " ")
			return transformer
		})
	_, initial := testPropagateStore(ctx, t, store, input)
	revertTransformer()

        this.pluginConfigurationExpander = pluginConfigurationExpander;
        this.profileActivationFilePathInterpolator = profileActivationFilePathInterpolator;
        this.transformer = transformer;
        this.versionParser = versionParser;
    }

    @Override
    public ModelTransformerContextBuilder newTransformerContextBuilder() {
        return new DefaultModelTransformerContextBuilder(this);

    private static class ActivationWalker extends MavenTransformer {

        private final Deque<ActivationFrame> stk;

        ActivationWalker(Deque<ActivationFrame> stk, UnaryOperator<String> transformer) {
            super(transformer);
            this.stk = stk;
        }

        private ActivationFrame nextFrame(String property) {
            return new ActivationFrame(property, Optional.empty());
        }

    private static class ActivationWalker extends MavenTransformer {

        private final Deque<ActivationFrame> stk;

        ActivationWalker(Deque<ActivationFrame> stk, UnaryOperator<String> transformer) {
            super(transformer);
            this.stk = stk;
        }

        private ActivationFrame nextFrame(String property) {
            return new ActivationFrame(property, Optional.empty());
        }

 * limitations under the License.
 */

package org.gradle.api.internal.provider

import com.google.common.collect.ImmutableCollection
import org.gradle.api.Task
import org.gradle.api.Transformer
import org.gradle.api.provider.Property
import org.gradle.api.provider.Provider
import org.gradle.internal.Describables
import org.gradle.util.internal.TextUtil
import org.spockframework.lang.Wildcard

 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.gradle.api.internal.file.collections


import org.gradle.api.Task
import org.gradle.api.Transformer
import org.gradle.api.file.FileCollection
import org.gradle.api.internal.file.AbstractFileCollection
import org.gradle.api.internal.file.FileCollectionInternal
import org.gradle.api.internal.file.FileCollectionSpec

 * limitations under the License.
 */

package org.gradle.api.internal.provider

import com.google.common.collect.ImmutableMap
import org.gradle.api.Task
import org.gradle.api.Transformer
import org.gradle.api.provider.MapProperty
import org.gradle.api.provider.Property
import org.gradle.api.provider.Provider
import org.gradle.internal.Describables
import org.gradle.internal.state.ManagedFactory

			return obj, nil
		}), nil); err != nil {
		t.Fatalf("GuaranteedUpdate failed: %v", err)
	}

	// Now trigger watch error by injecting failing transformer.
	revertTransformer := store.UpdatePrefixTransformer(
		func(previousTransformer *PrefixTransformer) value.Transformer {
			return &failingTransformer{}
		})
	defer revertTransformer()

* one takes a `{javaApi}/java/io/FilterReader.html[FilterReader]` and is designed to work with Ant filters, such as `ReplaceTokens`
* one takes a closure or link:{javadocPath}/org/gradle/api/Transformer.html[Transformer] that defines the transformation for each line of the source file

Note that both variants assume the source files are text-based.