Struct Expr 

pub struct Expr { /* private fields */ }

A CEL expression node in the abstract syntax tree.

Expr represents a single node in a CEL expression tree during macro expansion. Each expression has a unique ID for source location tracking and an optional kind that determines what type of expression it is (constant, function call, etc.).

Structure

An expression consists of:

• id: A unique identifier for source position tracking and error reporting
• kind: The specific type and content of the expression (or None for unspecified)

Expression Kinds

The kind field determines the expression type:

• Constant: Literal values (numbers, strings, booleans, etc.)
• IdentExpr: Variable or identifier references
• SelectExpr: Field selection (e.g., obj.field)
• CallExpr: Function or method calls
• ListExpr: List literals (e.g., [1, 2, 3])
• StructExpr: Struct literals (e.g., Person{name: "Alice"})
• MapExpr: Map literals (e.g., {"key": "value"})
• ComprehensionExpr: List/map comprehensions

Examples

// Access expression properties
let id = expr.id();
 
// Check expression kind
if let Some(kind) = expr.kind() {
    match kind {
        ExprKind::Constant(c) => println!("Constant: {:?}", c),
        ExprKind::Ident(i) => println!("Identifier: {}", i.name),
        ExprKind::Call(c) => println!("Function: {}", c.function),
        _ => {}
    }
}

Implementations

impl Expr

pub fn id(&self) -> i64

Returns the unique identifier of this expression.

Expression IDs are used for source location tracking and correlating expressions with their positions in the original source code.

pub fn set_id(&mut self, id: i64)

Sets the unique identifier of this expression.

This is typically handled by expression factory methods and rarely needs to be called directly in user code.

pub fn kind(&self) -> Option<&ExprKind>

Returns a reference to the expression kind, if set.

Returns None for unspecified expressions (expressions without a kind set).

Examples

if let Some(kind) = expr.kind() {
    if kind.is_constant() {
        println!("This is a constant expression");
    }
}

pub fn set_kind(&mut self, kind: ExprKind)

Sets the expression kind.

This replaces any existing kind with the new one. Use this to construct or modify expressions during macro expansion.

pub fn clear_kind(&mut self)

Clears the expression kind, making this an unspecified expression.

This is rarely needed in practice; most expressions should have a kind.

Methods from Deref<Target = ExprKind>

pub fn is_constant(&self) -> bool

Returns true if this is a constant expression.

pub fn is_ident(&self) -> bool

Returns true if this is an identifier expression.

pub fn is_select(&self) -> bool

Returns true if this is a select expression.

pub fn is_call(&self) -> bool

Returns true if this is a call expression.

pub fn is_list(&self) -> bool

Returns true if this is a list expression.

pub fn is_struct(&self) -> bool

Returns true if this is a struct expression.

pub fn is_map(&self) -> bool

Returns true if this is a map expression.

pub fn is_comprehension(&self) -> bool

Returns true if this is a comprehension expression.

pub fn as_constant(&self) -> Option<&Constant>

Returns a reference to the constant value if this is a constant expression.

pub fn as_ident(&self) -> Option<&IdentExpr>

Returns a reference to the identifier if this is an identifier expression.

pub fn as_select(&self) -> Option<&SelectExpr>

Returns a reference to the select expression if this is a select expression.

pub fn as_call(&self) -> Option<&CallExpr>

Returns a reference to the call expression if this is a call expression.

pub fn as_list(&self) -> Option<&ListExpr>

Returns a reference to the list expression if this is a list expression.

pub fn as_struct(&self) -> Option<&StructExpr>

Returns a reference to the struct expression if this is a struct expression.

pub fn as_map(&self) -> Option<&MapExpr>

Returns a reference to the map expression if this is a map expression.

pub fn as_comprehension(&self) -> Option<&ComprehensionExpr>

Returns a reference to the comprehension expression if this is a comprehension expression.

pub fn as_constant_mut(&mut self) -> Option<&mut Constant>

Returns a mutable reference to the constant value if this is a constant expression.

pub fn as_ident_mut(&mut self) -> Option<&mut IdentExpr>

Returns a mutable reference to the identifier if this is an identifier expression.

pub fn as_select_mut(&mut self) -> Option<&mut SelectExpr>

Returns a mutable reference to the select expression if this is a select expression.

pub fn as_call_mut(&mut self) -> Option<&mut CallExpr>

Returns a mutable reference to the call expression if this is a call expression.

pub fn as_list_mut(&mut self) -> Option<&mut ListExpr>

Returns a mutable reference to the list expression if this is a list expression.

pub fn as_struct_mut(&mut self) -> Option<&mut StructExpr>

Returns a mutable reference to the struct expression if this is a struct expression.

pub fn as_map_mut(&mut self) -> Option<&mut MapExpr>

Returns a mutable reference to the map expression if this is a map expression.

pub fn as_comprehension_mut(&mut self) -> Option<&mut ComprehensionExpr>

Returns a mutable reference to the comprehension expression if this is a comprehension expression.

Trait Implementations

impl Debug for Expr

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Expr

fn default() -> Expr

Returns the “default value” for a type.

impl Deref for Expr

type Target = ExprKind

The resulting type after dereferencing.

fn deref(&self) -> &Self::Target

Dereferences the value.

impl DerefMut for Expr

fn deref_mut(&mut self) -> &mut Self::Target

Mutably dereferences the value.

impl From<&Expr> for Expr

fn from(value: &Expr) -> Self

Converts to this type from the input type.

impl From<&Expr> for UniquePtr<Expr>

fn from(value: &Expr) -> Self

Converts to this type from the input type.

impl From<Expr> for UniquePtr<Expr>

fn from(value: Expr) -> Self

Converts to this type from the input type.

impl From<UniquePtr<Expr>> for Expr

fn from(value: UniquePtr<Expr>) -> Self

Converts to this type from the input type.