Add implicit false for missing variables in conditionals #318
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Add opt-in feature to treat undefined variables as false in conditional
statements instead of throwing errors. This provides a more convenient
syntax similar to JavaScript/Python where missing properties can be
checked directly.
Usage:
env.set_implicit_false_for_missing_vars(true);
// Now: {% if entity.Person %} works even if Person doesn't exist
// Instead of: {% if existsIn(entity, "Person") %}
Key implementation details:
- Added RenderConfig::implicit_false_for_missing_vars flag (defaults to false)
- Modified eval_expression_list() to accept allow_missing parameter
- Extended logical operators (and, or, not) to handle missing variables
- Feature only applies to conditionals, not expressions or loops
- Thread-safe: config is const member copied per render call
Testing:
- 21 new test assertions covering all subcases
- Tests default behavior, missing variables, existing variables,
logical operators, else-if chains, loops, and deep nesting
- All 279 assertions pass (21 new + 258 existing)
- No regressions in existing functionality
Documentation:
- Comprehensive guide in IMPLICIT_FALSE_FEATURE.md
- Brief usage example added to README.md
This feature is 100% backward compatible as it defaults to disabled.
Add opt-in environment flag to automatically wrap non-array values in arrays
when used in for loops. This solves the common XML-to-JSON cardinality problem
where single items are objects but multiple items are arrays.
Problem solved:
- XML with one <person> converts to object: {"person": {...}}
- XML with multiple <person> converts to array: {"person": [{...}, {...}]}
- Previously required different templates or custom ensureArray() callback
- Now no custom code is needed to use a for loop with json objects that change cardinality per request.
Usage:
env.set_ensure_array_for_loops(true);
// {% for p in person %} now works whether person is object or array
Implementation:
- Added RenderConfig::ensure_array_for_loops flag (defaults to false)
- Added Environment::set_ensure_array_for_loops() method
- Created ensure_array() helper function that wraps non-arrays:
* Arrays: returned unchanged
* Null: becomes empty array []
* Objects/primitives: wrapped in single-item array [value]
- Modified ForArrayStatementNode::visit() to call ensure_array() when enabled
Testing:
- 26 new test assertions in test-ensure-array.cpp
- Tests single objects, arrays, null, primitives, nested loops
- Tests default behavior, enabled behavior, and disabled flag
- All 284 assertions pass (26 new + 258 existing)
- No regressions in existing functionality
- Stress tested with 10,000 iterations
Backward compatibility:
- 100% backward compatible - flag defaults to false
- Without explicit enablement, behavior is identical to previous versions
- Non-arrays still throw errors by default
- Existing code requires zero changes
Documentation:
- Added usage example to README.md
- Comprehensive test suite demonstrates all use cases
Add ensure_array_for_loops feature for XML-to-JSON compatibility
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Add opt-in feature to treat undefined variables as false in conditional statements instead of throwing errors. This provides a more convenient syntax similar to JavaScript/Python where missing properties can be checked directly.
Usage:
env.set_implicit_false_for_missing_vars(true);
// Now: {% if entity.Person %} works even if Person doesn't exist
// Instead of: {% if existsIn(entity, "Person") %}
Key implementation details:
Testing:
Documentation:
This feature is 100% backward compatible as it defaults to disabled.