Functions

function 反射和注册

io.trino.operator.scalar.annotations.ScalarFromAnnotationsParser

这里是提取注解元素的方法
String baseName = scalarFunction.value().isEmpty() ? camelToSnake(annotatedName(annotated)) : scalarFunction.value();

这里如果 scalarFunction 的注解没有没有值，直接对函数名进行snake命名法

一般程序设计中，有两种变量命名规范：Snake方式和Camel方式。

• Snake方式是指单词用小写字母，单词间下划线（“_”）代替空格；
• Camel方式是指相邻单词首字母用大写表示，对单词加以区分。

例如，你想定义一个变量表示一个数组数字之和，并且用英文“sum of array”。我们使用Snake方式的变量名为：sum_of_array；用Camel命名方式的变量名为：sumOfArray。

  public static List<ScalarImplementationHeader> fromAnnotatedElement(AnnotatedElement annotated)
    {
        ScalarFunction scalarFunction = annotated.getAnnotation(ScalarFunction.class);
        ScalarOperator scalarOperator = annotated.getAnnotation(ScalarOperator.class);
        Optional<String> description = parseDescription(annotated);

        ImmutableList.Builder<ScalarImplementationHeader> builder = ImmutableList.builder();

        if (scalarFunction != null) {
            String baseName = scalarFunction.value().isEmpty() ? camelToSnake(annotatedName(annotated)) : scalarFunction.value();
            builder.add(new ScalarImplementationHeader(baseName, new ScalarHeader(description, scalarFunction.hidden(), scalarFunction.deterministic())));

            for (String alias : scalarFunction.alias()) {
                builder.add(new ScalarImplementationHeader(alias, new ScalarHeader(description, scalarFunction.hidden(), scalarFunction.deterministic())));
            }
        }

        if (scalarOperator != null) {
            builder.add(new ScalarImplementationHeader(scalarOperator.value(), new ScalarHeader(description, true, true)));
        }

        List<ScalarImplementationHeader> result = builder.build();
        checkArgument(!result.isEmpty());
        return result;
    }

io.trino.operator.scalar.annotations.ScalarImplementationHeader

private static String annotatedName(AnnotatedElement annotatedElement)
    {
        if (annotatedElement instanceof Class<?>) {
            return ((Class<?>) annotatedElement).getSimpleName();
        }
        if (annotatedElement instanceof Method) {
            return ((Method) annotatedElement).getName();
        }

        checkArgument(false, "Only Classes and Methods are supported as annotated elements.");
        return null;
    }

由上可得 method 也是一种 AnnotatedElement

trino 中的 snake 命名法

io.trino.operator.scalar.annotations.ScalarImplementationHeader

private static String camelToSnake(String name)
    {
        return LOWER_CAMEL.to(LOWER_UNDERSCORE, name);
    }

com.google.common.base.CaseFormat

  /**
   * Converts the specified {@code String str} from this format to the specified {@code format}. A
   * "best effort" approach is taken; if {@code str} does not conform to the assumed format, then
   * the behavior of this method is undefined but we make a reasonable effort at converting anyway.
   */
  public final String to(CaseFormat format, String str) {
    checkNotNull(format);
    checkNotNull(str);
    return (format == this) ? str : convert(format, str);
  }

  /** Enum values can override for performance reasons. */
  String convert(CaseFormat format, String s) {
    // deal with camel conversion
    StringBuilder out = null;
    int i = 0;
    int j = -1;
    while ((j = wordBoundary.indexIn(s, ++j)) != -1) {
      if (i == 0) {
        // include some extra space for separators
        out = new StringBuilder(s.length() + 4 * format.wordSeparator.length());
        out.append(format.normalizeFirstWord(s.substring(i, j)));
      } else {
        requireNonNull(out).append(format.normalizeWord(s.substring(i, j)));
      }
      out.append(format.wordSeparator);
      i = j + wordSeparator.length();
    }
    return (i == 0)
        ? format.normalizeFirstWord(s)
        : requireNonNull(out).append(format.normalizeWord(s.substring(i))).toString();
  }