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References (OSP)#

Code Example

Runnable Example in Jac and JacLib

"""References (OSP): Reference operator (&) for pass-by-reference semantics."""

with entry {
    # The & operator creates a reference to a variable
    # This is currently unused/deprecated in Jac but defined in grammar

    x = 42;

    # Note: BW_AND as reference operator is in grammar but may not be active
    # The ref rule: BW_AND? pipe_call allows optional & prefix
    # Example (if supported): ref_x = &x;

    print("Reference operator & is defined in grammar (ref rule) but currently unused");
}

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"""References (OSP): Reference operator (&) for pass-by-reference semantics."""

with entry {
    # The & operator creates a reference to a variable
    # This is currently unused/deprecated in Jac but defined in grammar

    x = 42;

    # Note: BW_AND as reference operator is in grammar but may not be active
    # The ref rule: BW_AND? pipe_call allows optional & prefix
    # Example (if supported): ref_x = &x;

    print("Reference operator & is defined in grammar (ref rule) but currently unused");
}

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from __future__ import annotations
from jaclang.runtimelib.builtin import *
x = 42
print('Reference operator & is defined in grammar (ref rule) but currently unused')
Jac Grammar Snippet 
297
ref: BW_AND? pipe_call

Description

Reference Operator with BW_AND (&) - Unused Feature

This file documents the & (BW_AND) operator as a reference operator, which is defined in Jac's grammar but is currently unused or deprecated.

What This Example Shows

Line 7 demonstrates a simple variable assignment where x is set to 42. The example notes that while the grammar includes a reference operator syntax using &, this feature is not currently active in Jac. Line 13 explicitly states that the reference operator & is defined in the grammar but remains unused.

Grammar Definition

Lines 9-10 explain the grammar rule that defines this unused feature. The ref rule in Jac's grammar uses the pattern BW_AND? pipe_call, where the ? indicates the & prefix is optional. This means syntax like &x would be recognized by the parser, but it doesn't have active runtime behavior.

Current Status

Aspect Status
Grammar Support Defined (BW_AND? allows optional & prefix)
Parser Recognition Yes (syntax is valid)
Runtime Behavior No (feature is inactive)
Recommended Usage Do not use in production code

Why It's Unused

Jac follows Python's reference semantics model where: - Variables automatically hold references to objects - Assignment creates new references to the same object - Explicit reference operators are unnecessary

Languages like C++ use & for explicit references, but Python-influenced languages like Jac make this redundant since reference semantics are built into the object model.

Practical Implications

For developers working with Jac: - Avoid using the & operator in your code - Use standard variable assignment instead - The grammar may include this for parsing compatibility - Future versions might remove it or give it new meaning

Historical Context

The presence of this unused operator suggests it was considered during language design. Many programming languages evolve away from explicit reference operators when adopting implicit reference semantics, similar to how Python, JavaScript, and Ruby work compared to C/C++.