mirror of
https://github.com/honeymoose/OpenSearch.git
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3a7a218e8f
Adds support for indexing into lists and arrays with negative indexes meaning "counting from the back". So for if `x = ["cat", "dog", "chicken"]` then `x[-1] == "chicken"`. This adds an extra branch to every array and list access but some performance testing makes it look like the branch predictor successfully predicts the branch every time so there isn't a in execution time for this feature when the index is positive. When the index is negative performance testing showed the runtime is the same as writing `x[x.length - 1]`, again, presumably thanks to the branch predictor. Those performance metrics were calculated for lists and arrays but `def`s get roughly the same treatment though instead of inlining the test they need to make a invoke dynamic so we don't screw up maps. Closes #20870
193 lines
6.2 KiB
Plaintext
193 lines
6.2 KiB
Plaintext
[[modules-scripting-painless-syntax]]
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=== Painless Syntax
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experimental[The Painless scripting language is new and is still marked as experimental. The syntax or API may be changed in the future in non-backwards compatible ways if required.]
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[float]
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[[painless-types]]
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=== Variable types
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Painless supports all of https://docs.oracle.com/javase/tutorial/java/nutsandbolts/variables.html[Java's types],
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including array types, but adds some additional built-in types.
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[float]
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[[painless-def]]
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==== Def
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The dynamic type `def` serves as a placeholder for any other type. It adopts the behavior
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of whatever runtime type it represents.
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[float]
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[[painless-strings]]
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==== String
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String constants can be declared with single quotes, to avoid escaping horrors with JSON:
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[source,painless]
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---------------------------------------------------------
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def mystring = 'foo';
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---------------------------------------------------------
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[float]
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[[painless-arrays]]
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==== Arrays
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Arrays can be subscripted starting from `0` for traditional array access or with
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negative numbers to starting from the back of the array. So the following
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returns `2`.
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[source,painless]
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---------------------------------------------------------
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int[] x = new int[5];
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x[0]++;
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x[-5]++;
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return x[0];
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---------------------------------------------------------
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[float]
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[[painless-lists]]
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==== List
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Lists can be created explicitly (e.g. `new ArrayList()`) or initialized similar to Groovy:
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[source,painless]
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---------------------------------------------------------
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def list = [1,2,3];
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---------------------------------------------------------
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Lists can also be accessed similar to arrays. They support `.length` and
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subscripts, including negative subscripts to read from the back of the list:
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[source,painless]
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---------------------------------------------------------
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def list = [1,2,3];
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list[-1] = 5
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return list[0]
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---------------------------------------------------------
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[float]
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[[painless-maps]]
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==== Map
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Maps can be created explicitly (e.g. `new HashMap()`) or initialized similar to Groovy:
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[source,painless]
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---------------------------------------------------------
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def person = ['name': 'Joe', 'age': 63];
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---------------------------------------------------------
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Map keys can also be accessed as properties.
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[source,painless]
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---------------------------------------------------------
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def person = ['name': 'Joe', 'age': 63];
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person.retired = true;
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return person.name
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---------------------------------------------------------
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Map keys can also be accessed via subscript (for keys containing special characters):
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[source,painless]
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---------------------------------------------------------
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return map['something-absurd!']
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---------------------------------------------------------
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[float]
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[[painless-pattern]]
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==== Pattern
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Regular expression constants are directly supported:
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[source,painless]
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---------------------------------------------------------
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Pattern p = /[aeiou]/
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---------------------------------------------------------
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Patterns can only be created via this mechanism. This ensures fast performance, regular expressions
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are always constants and compiled efficiently a single time.
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[float]
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[[modules-scripting-painless-regex-flags]]
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==== Pattern flags
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You can define flags on patterns in Painless by adding characters after the
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trailing `/` like `/foo/i` or `/foo \w #comment/iUx`. Painless exposes all the
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flags from
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https://docs.oracle.com/javase/8/docs/api/java/util/regex/Pattern.html[Java's Pattern class]
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using these characters:
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[cols="<,<,<",options="header",]
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|=======================================================================
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| Character | Java Constant | Example
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|`c` | CANON_EQ | `'å' ==~ /å/c` (open in hex editor to see)
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|`i` | CASE_INSENSITIVE | `'A' ==~ /a/i`
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|`l` | LITERAL | `'[a]' ==~ /[a]/l`
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|`m` | MULTILINE | `'a\nb\nc' =~ /^b$/m`
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|`s` | DOTALL (aka single line) | `'a\nb\nc' =~ /.b./s`
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|`U` | UNICODE_CHARACTER_CLASS | `'Ɛ' ==~ /\\w/U`
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|`u` | UNICODE_CASE | `'Ɛ' ==~ /ɛ/iu`
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|`x` | COMMENTS (aka extended) | `'a' ==~ /a #comment/x`
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|=======================================================================
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[float]
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[[painless-operators]]
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=== Operators
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All of Java's https://docs.oracle.com/javase/tutorial/java/nutsandbolts/operators.html[operators] are
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supported with the same precedence, promotion, and semantics.
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There are only a few minor differences and add-ons:
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* `==` behaves as Java's for numeric types, but for non-numeric types acts as https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#equals-java.lang.Object-[`Object.equals()`]
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* `===` and `!==` support exact reference comparison (e.g. `x === y`)
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* `=~` true if a portion of the text matches a pattern (e.g. `x =~ /b/`)
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* `==~` true if the entire text matches a pattern (e.g. `x ==~ /[Bb]ob/`)
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[float]
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[[painless-control-flow]]
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=== Control flow
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Java's https://docs.oracle.com/javase/tutorial/java/nutsandbolts/flow.html[control flow statements] are supported, with the exception
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of the `switch` statement.
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In addition to Java's `enhanced for` loop, the `for in` syntax from groovy can also be used:
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[source,painless]
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---------------------------------------------------------
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for (item : list) {
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...
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}
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---------------------------------------------------------
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[float]
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[[painless-functions]]
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=== Functions
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Functions can be declared at the beginning of the script, for example:
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[source,painless]
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---------------------------------------------------------
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boolean isNegative(def x) { x < 0 }
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...
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if (isNegative(someVar)) {
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...
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}
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---------------------------------------------------------
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[float]
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[[painless-lambda-expressions]]
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=== Lambda expressions
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Lambda expressions and method references work the same as https://docs.oracle.com/javase/tutorial/java/javaOO/lambdaexpressions.html[Java's].
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[source,painless]
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---------------------------------------------------------
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list.removeIf(item -> item == 2);
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list.removeIf((int item) -> item == 2);
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list.removeIf((int item) -> { item == 2 });
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list.sort((x, y) -> x - y);
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list.sort(Integer::compare);
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---------------------------------------------------------
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Method references to functions within the script can be accomplished using `this`, e.g. `list.sort(this::mycompare)`.
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