package org.checkerframework.checker.index.qual;
import java.lang.annotation.ElementType;
import java.lang.annotation.Target;
/**
* An integer that can be used to index any of the given sequences.
*
* <p>For example, an expression with type {@code @IndexFor({"a", "b"})} is non-negative and is less
* than both {@code a.length} and {@code b.length}. The sequences {@code a} and {@code b} might have
* different lengths.
*
* <p>The <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/String.html#charAt-int-">
* <code>String.charAt(int)</code></a> method is declared as
*
* <pre>{@code
* class String {
* char charAt(@IndexFor("this") index) { ... }
* }
* }</pre>
*
* <p>Writing {@code @IndexFor("arr")} is equivalent to writing {@link NonNegative @NonNegative}
* {@link LTLengthOf @LTLengthOf("arr")}, and that is how it is treated internally by the checker.
* Thus, if you write an {@code @IndexFor("arr")} annotation, you might see warnings about
* {@code @NonNegative} or {@code @LTLengthOf}.
*
* @see NonNegative
* @see LTLengthOf
* @checker_framework.manual #index-checker Index Checker
*/
@Target({ElementType.TYPE_USE, ElementType.TYPE_PARAMETER})
public @interface IndexFor {
/** Sequences that the annotated expression is a valid index for. */
String[] value() default {};
}