org.graalvm.nativeimage.c.constant.CConstant Maven / Gradle / Ivy
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package org.graalvm.nativeimage.c.constant;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.graalvm.nativeimage.ImageSingletons;
import org.graalvm.nativeimage.Platform;
import org.graalvm.nativeimage.Platforms;
import org.graalvm.nativeimage.c.CContext;
import org.graalvm.nativeimage.impl.CConstantValueSupport;
/**
* Denotes a method as a C constant value.
*
* Calls to the method are replaced with a compile time constant. The constant value is extracted
* from the C header file during native image generation.
*
* The class containing the annotated method must be annotated with {@link CContext}.
*/
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD})
public @interface CConstant {
/**
* Specifies the name of the C constant. If no name is provided, the method name is used as the
* field name. A possible "get" prefix of the method name is removed.
*/
String value() default "";
final class ValueAccess {
private ValueAccess() {
}
/**
* Returns the value of a {@link CConstant}, i.e., the same value that calling the annotated
* method would return.
*
* This method is useful during native image generation, when the annotated method cannot be
* called.
*
* @param declaringClass The class that contains the method annotated with {@link CConstant}
* .
* @param methodName The name of the method annotated with {@link CConstant}.
* @param returnType The desired type of the returned value. For integer-kind constants, the
* supported types are {@link Long}, {@link Integer}, and {@link Boolean}. For
* floating point constants, the only supported type is {@link Double}. For
* string constants, the only supported type is {@link String}.
* @return The value of the C constant.
*/
@Platforms(Platform.HOSTED_ONLY.class)
public static T get(Class declaringClass, String methodName, Class returnType) {
return ImageSingletons.lookup(CConstantValueSupport.class).getCConstantValue(declaringClass, methodName, returnType);
}
}
}