Expression.Comprehension

All Known Implementing Classes:

CelExpr.CelComprehension

Enclosing interface:

Expression
```
public static interface Expression.Comprehension<E extends Expression>
```
A comprehension expression applied to a list or map.
Comprehensions are not part of the core syntax, but enabled with macros. A macro matches a specific call signature within a parsed AST and replaces the call with an alternate AST block. Macro expansion happens at parse time.
The following macros are supported within CEL:
Aggregate type macros may be applied to all elements in a list or all keys in a map:
`all`, `exists`, `exists_one` - test a predicate expression against the inputs and return `true` if the predicate is satisfied for all, any, or only one value `list.all(x, x < 10)`. `filter` - test a predicate expression against the inputs and return the subset of elements which satisfy the predicate: `payments.filter(p, p > 1000)`. `map` - apply an expression to all elements in the input and return the output aggregate type: `[1, 2, 3].map(i, i * i)`.
The `has(m.x)` macro tests whether the property `x` is present in struct `m`. The semantics of this macro depend on the type of `m`. For proto2 messages `has(m.x)` is defined as 'defined, but not set`. For proto3, the macro tests whether the property is set to its default. For map and struct types, the macro tests whether the property `x` is defined on `m`.
Comprehension evaluation can be best visualized as the following pseudocode:

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`E`	`accuInit()`	The initial value of the accumulator.
`java.lang.String`	`accuVar()`	The name of the variable used for accumulation of the result.
`E`	`iterRange()`	The range over which var iterates.
`java.lang.String`	`iterVar()`	The name of the iteration variable.
`E`	`loopCondition()`	An expression which can contain iter_var and accu_var.
`E`	`loopStep()`	An expression which can contain iter_var and accu_var.
`E`	`result()`	An expression which can contain accu_var.

- Method Detail
  - iterVar
```
java.lang.String iterVar()
```
    The name of the iteration variable.
  - iterRange
```
E iterRange()
```
    The range over which var iterates.
  - accuVar
```
java.lang.String accuVar()
```
    The name of the variable used for accumulation of the result.
  - accuInit
```
E accuInit()
```
    The initial value of the accumulator.
  - loopCondition
```
E loopCondition()
```
    An expression which can contain iter_var and accu_var.
    Returns false when the result has been computed and may be used as a hint to short-circuit the remainder of the comprehension.
  - loopStep
```
E loopStep()
```
    An expression which can contain iter_var and accu_var.
    Computes the next value of accu_var.
  - result
```
E result()
```
    An expression which can contain accu_var.
    Computes the result.