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Substrate VM re-uses much of the Graal option system for handling its own options. In the Graal option system, an option is declared as a static final field that is annotated with the annotation Option. Values are stored in OptionValues. 

Substrate VM has two distinct kinds of options:

Hosted options: configure the native image generation, i.e., influence what is put into the
image and how the image is built. They are set using the prefix -H: on the command line. Options are defined using fields of the class HostedOptionKey. The option values are maintained by HostedOptionValues. The most convenient access to the value of a hosted option is HostedOptionKey.getValue(). 
 Hosted options cannot be changed at run time. Instead they are guaranteed to be constant folded in the image. This is implemented using the Fold annotation on HostedOptionKey.getValue().
Runtime options: get their initial value during native image generation, using the prefix
-R: on the command line. Options are defined using fields of the class RuntimeOptionKey. The option values are maintained by RuntimeOptionValues. The most convenient access to the value of a runtime option is RuntimeOptionKey.getValue(). 
 Runtime options can be changed at run time. RuntimeOptionParser.parse is a convenient helper to do option parsing at run time.
 Substrate VM re-uses much of the Graal option system for handling. However, Graal itself is stateless, i.e, every Graal compilation can be configured with its own set of OptionValues. Therefore, access of a Graal option using OptionKey.getValue(OptionValues) requires to explicitly specify one of the two option values of Substrate VM: HostedOptionValues.singleton() or RuntimeOptionValues.singleton(). /**
 * Substrate VM re-uses much of the Graal option system for handling its own options. In the Graal
 * option system, an option is declared as a {@code static final} field that is annotated with the
 * annotation {@link org.graalvm.compiler.options.Option}. Values are stored in
 * {@link org.graalvm.compiler.options.OptionValues}.
 * <p>
 * Substrate VM has two distinct kinds of options:
 * <ul>
 * <li>Hosted options: configure the native image generation, i.e., influence what is put into the
 * image and how the image is built. They are set using the prefix <b>-H:</b> on the command line.
 * Options are defined using fields of the class {@link com.oracle.svm.core.option.HostedOptionKey}.
 * The option values are maintained by {@link com.oracle.svm.core.option.HostedOptionValues}. The
 * most convenient access to the value of a hosted option is
 * {@link com.oracle.svm.core.option.HostedOptionKey#getValue()}.
 * <p>
 * Hosted options cannot be changed at run time. Instead they are guaranteed to be constant folded
 * in the image. This is implemented using the {@link org.graalvm.compiler.api.replacements.Fold}
 * annotation on {@link com.oracle.svm.core.option.HostedOptionKey#getValue()}.</li>
 *
 * <li>Runtime options: get their initial value during native image generation, using the prefix
 * <b>-R:</b> on the command line. Options are defined using fields of the class
 * {@link com.oracle.svm.core.option.RuntimeOptionKey}. The option values are maintained by
 * {@link com.oracle.svm.core.option.RuntimeOptionValues}. The most convenient access to the value
 * of a runtime option is {@link com.oracle.svm.core.option.RuntimeOptionKey#getValue()}.
 * <p>
 * Runtime options can be changed at run time.
 * {@link com.oracle.svm.core.option.RuntimeOptionParser#parse} is a convenient helper to do option
 * parsing at run time.</li>
 * </ul>
 *
 * Substrate VM re-uses much of the Graal option system for handling. However, Graal itself is
 * stateless, i.e, every Graal compilation can be configured with its own set of
 * {@link org.graalvm.compiler.options.OptionValues}. Therefore, access of a Graal option using
 * {@link org.graalvm.compiler.options.OptionKey#getValue(org.graalvm.compiler.options.OptionValues)}
 * requires to explicitly specify one of the two option values of Substrate VM:
 * {@link com.oracle.svm.core.option.HostedOptionValues#singleton()} or
 * {@link com.oracle.svm.core.option.RuntimeOptionValues#singleton()}.
 */
package com.oracle.svm.core.option;