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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 CContext. 
Since:
19.0/**
 * Denotes a method as a C constant value.
 * <p>
 * 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.
 * <p>
 * The class containing the annotated method must be annotated with {@link CContext}.
 *
 * @since 19.0
 */
@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.
Since:
19.0/**
     * 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.
     *
     * @since 19.0
     */
    String value() default "";

    
Allows access to the value of a CConstant during image generation. 
Since:
19.0/**
     * Allows access to the value of a {@link CConstant} during image generation.
     *
     * @since 19.0
     */
    final class ValueAccess {
        private ValueAccess() {
        }

        
Returns the value of a 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.
Params:
declaringClass – The class that contains the method annotated with CConstant .
methodName – The name of the method annotated with CConstant.
returnType – The desired type of the returned value. For integer-kind constants, the supported types are Long, Integer, and Boolean. For floating point constants, the only supported type is Double. For string constants, the only supported type is String.
Returns:
The value of the C constant.
Since:
19.0/**
         * Returns the value of a {@link CConstant}, i.e., the same value that calling the annotated
         * method would return.
         * <p>
         * 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.
         *
         * @since 19.0
         */
        @Platforms(Platform.HOSTED_ONLY.class)
        public static <T> T get(Class<?> declaringClass, String methodName, Class<T> returnType) {
            return ImageSingletons.lookup(CConstantValueSupport.class).getCConstantValue(declaringClass, methodName, returnType);
        }
    }
}