code: // ASM: a very small and fast Java bytecode manipulation framework
  // Copyright (c) 2000-2011 INRIA, France Telecom
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  package clojure.asm;
  
  /**
   * The path to a type argument, wildcard bound, array element type, or static inner type within an
   * enclosing type.
   *
   * @author Eric Bruneton
   */
  public class TypePath {
  
    /** A type path step that steps into the element type of an array type. See {@link #getStep}. */
    public static final int ARRAY_ELEMENT = 0;
  
    /** A type path step that steps into the nested type of a class type. See {@link #getStep}. */
    public static final int INNER_TYPE = 1;
  
    /** A type path step that steps into the bound of a wildcard type. See {@link #getStep}. */
    public static final int WILDCARD_BOUND = 2;
  
    /** A type path step that steps into a type argument of a generic type. See {@link #getStep}. */
    public static final int TYPE_ARGUMENT = 3;
  
    /**
     * The byte array where the 'type_path' structure - as defined in the Java Virtual Machine
     * Specification (JVMS) - corresponding to this TypePath is stored. The first byte of the
     * structure in this array is given by {@link #typePathOffset}.
     *
     * @see <a
     *     href="https://docs.oracle.com/javase/specs/jvms/se9/html/jvms-4.html#jvms-4.7.20.2">JVMS
     *     4.7.20.2</a>
     */
    private final byte[] typePathContainer;
  
    /** The offset of the first byte of the type_path JVMS structure in {@link #typePathContainer}. */
    private final int typePathOffset;
  
    /**
     * Constructs a new TypePath.
     *
     * @param typePathContainer a byte array containing a type_path JVMS structure.
     * @param typePathOffset the offset of the first byte of the type_path structure in
     *     typePathContainer.
     */
    TypePath(final byte[] typePathContainer, final int typePathOffset) {
      this.typePathContainer = typePathContainer;
      this.typePathOffset = typePathOffset;
    }
  
    /**
     * Returns the length of this path, i.e. its number of steps.
     *
     * @return the length of this path.
     */
    public int getLength() {
      // path_length is stored in the first byte of a type_path.
      return typePathContainer[typePathOffset];
    }
  
    /**
     * Returns the value of the given step of this path.
     *
     * @param index an index between 0 and {@link #getLength()}, exclusive.
     * @return one of {@link #ARRAY_ELEMENT}, {@link #INNER_TYPE}, {@link #WILDCARD_BOUND}, or {@link
     *     #TYPE_ARGUMENT}.
     */
    public int getStep(final int index) {
      // Returns the type_path_kind of the path element of the given index.
      return typePathContainer[typePathOffset + 2 * index + 1];
    }
  
    /**
     * Returns the index of the type argument that the given step is stepping into. This method should
     * only be used for steps whose value is {@link #TYPE_ARGUMENT}.
     *
     * @param index an index between 0 and {@link #getLength()}, exclusive.
     * @return the index of the type argument that the given step is stepping into.
     */
    public int getStepArgument(final int index) {
      // Returns the type_argument_index of the path element of the given index.
      return typePathContainer[typePathOffset + 2 * index + 2];
    }
  
    /**
     * Converts a type path in string form, in the format used by {@link #toString()}, into a TypePath
     * object.
     *
     * @param typePath a type path in string form, in the format used by {@link #toString()}. May be
     *     <tt>null</tt> or empty.
     * @return the corresponding TypePath object, or <tt>null</tt> if the path is empty.
     */
    public static TypePath fromString(final String typePath) {
      if (typePath == null || typePath.length() == 0) {
        return null;
      }
      int typePathLength = typePath.length();
      ByteVector output = new ByteVector(typePathLength);
      output.putByte(0);
      int typePathIndex = 0;
      while (typePathIndex < typePathLength) {
        char c = typePath.charAt(typePathIndex++);
        if (c == '[') {
          output.put11(ARRAY_ELEMENT, 0);
        } else if (c == '.') {
          output.put11(INNER_TYPE, 0);
        } else if (c == '*') {
          output.put11(WILDCARD_BOUND, 0);
        } else if (c >= '0' && c <= '9') {
          int typeArg = c - '0';
          while (typePathIndex < typePathLength) {
            c = typePath.charAt(typePathIndex++);
            if (c >= '0' && c <= '9') {
              typeArg = typeArg * 10 + c - '0';
            } else if (c == ';') {
              break;
            } else {
              throw new IllegalArgumentException();
            }
          }
          output.put11(TYPE_ARGUMENT, typeArg);
        } else {
          throw new IllegalArgumentException();
        }
      }
      output.data[0] = (byte) (output.length / 2);
      return new TypePath(output.data, 0);
    }
  
    /**
     * Returns a string representation of this type path. {@link #ARRAY_ELEMENT} steps are represented
     * with '[', {@link #INNER_TYPE} steps with '.', {@link #WILDCARD_BOUND} steps with '*' and {@link
     * #TYPE_ARGUMENT} steps with their type argument index in decimal form followed by ';'.
     */
    @Override
    public String toString() {
      int length = getLength();
      StringBuilder result = new StringBuilder(length * 2);
      for (int i = 0; i < length; ++i) {
        switch (getStep(i)) {
          case ARRAY_ELEMENT:
            result.append('[');
            break;
          case INNER_TYPE:
            result.append('.');
            break;
          case WILDCARD_BOUND:
            result.append('*');
            break;
          case TYPE_ARGUMENT:
            result.append(getStepArgument(i)).append(';');
            break;
          default:
            throw new AssertionError();
        }
      }
      return result.toString();
    }
  
    /**
     * Puts the type_path JVMS structure corresponding to the given TypePath into the given
     * ByteVector.
     *
     * @param typePath a TypePath instance, or <tt>null</tt> for empty paths.
     * @param output where the type path must be put.
     */
    static void put(final TypePath typePath, final ByteVector output) {
      if (typePath == null) {
        output.putByte(0);
      } else {
        int length = typePath.typePathContainer[typePath.typePathOffset] * 2 + 1;
        output.putByteArray(typePath.typePathContainer, typePath.typePathOffset, length);
      }
    }
  }
  