Module display_context 

Display context for formatting numbers with consistent precision.

This module provides the DisplayContext type which tracks a frequency distribution of decimal places per currency, observed during parsing. The configured Precision policy then determines how that distribution is collapsed to a single per-currency precision for display.

Default policy is Precision::MostCommon — the mode of the dp distribution. This matches Python bean-query’s default rendering and ensures that outliers (e.g. a single 28-decimal computed price annotation) don’t inflate the display precision for an otherwise 2dp-dominant currency.

Precision::Maximum selects the highest dp ever observed, which is what Python uses when rendering price tables. Callers opt in via DisplayContext::set_precision.

Example

use rustledger_core::DisplayContext;
use rust_decimal_macros::dec;

let mut ctx = DisplayContext::new();

// Track samples for USD: tied 1×0dp + 1×2dp → tie-break favors larger.
ctx.update(dec!(100), "USD");       // 0 dp
ctx.update(dec!(50.25), "USD");     // 2 dp
ctx.update(dec!(1.5), "EUR");       // 1 dp

// Default policy (MostCommon) returns the mode of the per-currency dist.
assert_eq!(ctx.get_precision("USD"), Some(2));
assert_eq!(ctx.get_precision("EUR"), Some(1));
assert_eq!(ctx.get_precision("GBP"), None); // Never seen

// format() uses the policy's effective precision.
assert_eq!(ctx.format(dec!(100), "USD"), "100.00");
assert_eq!(ctx.format(dec!(50.25), "USD"), "50.25");
assert_eq!(ctx.format(dec!(1.5), "EUR"), "1.5");

Structs

DisplayContext

Display context for formatting numbers with consistent precision per currency.

Enums

Precision

Policy for resolving the per-currency display precision from the observed distribution.

Constants

DEFAULT_CURRENCY

Sentinel currency key for “naked-decimal” observations.