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Allow partial evaluation of templates (#282)
* Defer evaluation of parts of templates * Handle deferring a whole TagNode * Add test for preserving function invocations * Also defer evaluation when encountering a random value * Update javadocs to use @link
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17 changes: 17 additions & 0 deletions
17
src/main/java/com/hubspot/jinjava/interpret/DeferredValue.java
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| @@ -0,0 +1,17 @@ | ||
| package com.hubspot.jinjava.interpret; | ||
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| /** | ||
| * Marker object which indicates that the template engine should skip over evaluating | ||
| * this part of the template, if the object is resolved from the context. | ||
| * | ||
| */ | ||
| public class DeferredValue { | ||
| private static final DeferredValue INSTANCE = new DeferredValue(); | ||
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| private DeferredValue() { | ||
| } | ||
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| public static DeferredValue instance() { | ||
| return INSTANCE; | ||
| } | ||
| } |
16 changes: 16 additions & 0 deletions
16
src/main/java/com/hubspot/jinjava/interpret/DeferredValueException.java
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,16 @@ | ||
| package com.hubspot.jinjava.interpret; | ||
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| /** | ||
| * Exception thrown when attempting to render a {@link com.hubspot.jinjava.interpret.DeferredValue}. | ||
| * The exception is effectively used for flow control, to unwind evaluating a template Node | ||
| * and instead echo its contents to the output. | ||
| */ | ||
| public class DeferredValueException extends InterpretException { | ||
| public DeferredValueException(String message) { | ||
| super("Encountered a deferred value: " + message); | ||
| } | ||
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| public DeferredValueException(String variable, int lineNumber, int startPosition) { | ||
| super("Encountered a deferred value: \"" + variable + "\"", lineNumber, startPosition); | ||
| } | ||
| } |
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121 changes: 121 additions & 0 deletions
121
src/main/java/com/hubspot/jinjava/random/DeferredRandomNumberGenerator.java
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| @@ -0,0 +1,121 @@ | ||
| package com.hubspot.jinjava.random; | ||
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| import java.util.Random; | ||
| import java.util.stream.DoubleStream; | ||
| import java.util.stream.IntStream; | ||
| import java.util.stream.LongStream; | ||
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| import com.hubspot.jinjava.interpret.DeferredValueException; | ||
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| /** | ||
| * A random number generator that throws {@link com.hubspot.jinjava.interpret.DeferredValueException} for all supported methods. | ||
| */ | ||
| public class DeferredRandomNumberGenerator extends Random { | ||
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| private static final String EXCEPTION_MESSAGE = "Generating random number"; | ||
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| @Override | ||
| protected int next(int bits) { | ||
| throw new DeferredValueException(EXCEPTION_MESSAGE); | ||
| } | ||
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| @Override | ||
| public int nextInt() { | ||
| throw new DeferredValueException(EXCEPTION_MESSAGE); | ||
| } | ||
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| @Override | ||
| public int nextInt(int bound) { | ||
| throw new DeferredValueException(EXCEPTION_MESSAGE); | ||
| } | ||
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| @Override | ||
| public long nextLong() { | ||
| throw new DeferredValueException(EXCEPTION_MESSAGE); | ||
| } | ||
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| @Override | ||
| public boolean nextBoolean() { | ||
| throw new DeferredValueException(EXCEPTION_MESSAGE); | ||
| } | ||
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| @Override | ||
| public float nextFloat() { | ||
| throw new DeferredValueException(EXCEPTION_MESSAGE); | ||
| } | ||
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| @Override | ||
| public double nextDouble() { | ||
| throw new DeferredValueException(EXCEPTION_MESSAGE); | ||
| } | ||
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| @Override | ||
| public synchronized double nextGaussian() { | ||
| throw new DeferredValueException(EXCEPTION_MESSAGE); | ||
| } | ||
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| @Override | ||
| public void nextBytes(byte[] bytes) { | ||
| throw new UnsupportedOperationException(); | ||
| } | ||
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| @Override | ||
| public IntStream ints(long streamSize) { | ||
| throw new UnsupportedOperationException(); | ||
| } | ||
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| @Override | ||
| public IntStream ints() { | ||
| throw new UnsupportedOperationException(); | ||
| } | ||
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| @Override | ||
| public IntStream ints(long streamSize, int randomNumberOrigin, int randomNumberBound) { | ||
| throw new UnsupportedOperationException(); | ||
| } | ||
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| @Override | ||
| public IntStream ints(int randomNumberOrigin, int randomNumberBound) { | ||
| throw new UnsupportedOperationException(); | ||
| } | ||
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| @Override | ||
| public LongStream longs(long streamSize) { | ||
| throw new UnsupportedOperationException(); | ||
| } | ||
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| @Override | ||
| public LongStream longs() { | ||
| throw new UnsupportedOperationException(); | ||
| } | ||
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| @Override | ||
| public LongStream longs(long streamSize, long randomNumberOrigin, long randomNumberBound) { | ||
| throw new UnsupportedOperationException(); | ||
| } | ||
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| @Override | ||
| public LongStream longs(long randomNumberOrigin, long randomNumberBound) { | ||
| throw new UnsupportedOperationException(); | ||
| } | ||
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| @Override | ||
| public DoubleStream doubles(long streamSize) { | ||
| throw new UnsupportedOperationException(); | ||
| } | ||
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| @Override | ||
| public DoubleStream doubles() { | ||
| throw new UnsupportedOperationException(); | ||
| } | ||
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| @Override | ||
| public DoubleStream doubles(long streamSize, double randomNumberOrigin, double randomNumberBound) { | ||
| throw new UnsupportedOperationException(); | ||
| } | ||
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| @Override | ||
| public DoubleStream doubles(double randomNumberOrigin, double randomNumberBound) { | ||
| throw new UnsupportedOperationException(); | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
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@@ -2,5 +2,6 @@ | |
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| public enum RandomNumberGeneratorStrategy { | ||
| THREAD_LOCAL, | ||
| CONSTANT_ZERO | ||
| CONSTANT_ZERO, | ||
| DEFERRED | ||
| } | ||
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