Struct FlexMeasurePolicy 

pub struct FlexMeasurePolicy {
    pub axis: Axis,
    pub main_axis_arrangement: LinearArrangement,
    pub cross_axis_alignment: CrossAxisAlignment,
}

Unified Flex layout policy that powers both Row and Column.

This policy implements Jetpack Compose’s flex layout semantics:

• Measures children with proper loose constraints (min = 0 on both axes)
• Supports weighted distribution of remaining space
• Handles bounded/unbounded main axis correctly
• Implements correct intrinsics for both axes

Overflow Behavior

Like Jetpack Compose, this policy allows children to overflow their container bounds:

• Children can be positioned outside the parent’s measured size
• Overflowing content is rendered (unless clipped by a modifier)
• When content overflows, distribution arrangements switch to Start to avoid negative spacing
• SpacedBy keeps its fixed inter-child spacing even when content overflows

Example: A Row with 300px of content in a 200px container will:

1. Measure children at their natural sizes
2. Detect overflow (300px > 200px)
3. Switch to Start arrangement (pack children at the start)
4. Position last children beyond the 200px boundary

To prevent overflow:

• Use weights for flexible sizing: .weight(1.0, true)
• Use fillMaxWidth()/fillMaxHeight() modifiers
• Design UI to fit within available space
• Add a clip modifier to hide overflowing content

Weighted Children

When the main axis is bounded and children have weights:

1. Fixed children (no weight) are measured first
2. Remaining space is distributed proportionally to weights
3. Each weighted child gets: remaining * (weight / total_weight)
4. If fill=true, child gets tight constraints; if fill=false, loose constraints

When the main axis is unbounded, weights are ignored (all children wrap content).

Fields

axis: Axis

Main axis direction (Horizontal for Row, Vertical for Column)

main_axis_arrangement: LinearArrangement

Arrangement along the main axis

cross_axis_alignment: CrossAxisAlignment

Alignment along the cross axis (used as default for children without explicit alignment)

Implementations

impl FlexMeasurePolicy

pub fn new( axis: Axis, main_axis_arrangement: LinearArrangement, cross_axis_alignment: CrossAxisAlignment, ) -> Self

pub fn row( horizontal_arrangement: LinearArrangement, vertical_alignment: VerticalAlignment, ) -> Self

Creates a FlexMeasurePolicy for Row (horizontal main axis).

pub fn column( vertical_arrangement: LinearArrangement, horizontal_alignment: HorizontalAlignment, ) -> Self

Creates a FlexMeasurePolicy for Column (vertical main axis).

Trait Implementations

impl Clone for FlexMeasurePolicy

fn clone(&self) -> FlexMeasurePolicy

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for FlexMeasurePolicy

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

Formats the value using the given formatter.

impl MeasurePolicy for FlexMeasurePolicy

fn measure( &self, measurables: &[Box<dyn Measurable>], constraints: Constraints, ) -> MeasureResult

Runs the measurement pass with the provided children and constraints.

fn measure_into( &self, measurables: &[Box<dyn Measurable>], constraints: Constraints, placements: &mut Vec<Placement>, ) -> Size

Runs measurement into caller-owned placement storage.

fn min_intrinsic_width( &self, measurables: &[Box<dyn Measurable>], height: f32, ) -> f32

Computes the minimum intrinsic width of this policy.

fn max_intrinsic_width( &self, measurables: &[Box<dyn Measurable>], height: f32, ) -> f32

Computes the maximum intrinsic width of this policy.

fn min_intrinsic_height( &self, measurables: &[Box<dyn Measurable>], width: f32, ) -> f32

Computes the minimum intrinsic height of this policy.

fn max_intrinsic_height( &self, measurables: &[Box<dyn Measurable>], width: f32, ) -> f32

Computes the maximum intrinsic height of this policy.

impl PartialEq for FlexMeasurePolicy

fn eq(&self, other: &FlexMeasurePolicy) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl StructuralPartialEq for FlexMeasurePolicy