fix tutorial

components/decimal/src/provider.rs

@@ -77,7 +77,9 @@ pub struct GroupingSizesV1 {
     pub min_grouping: u8,
 }
 
-/// The strings used in DecimalSymbolsV2
+/// A stack representation of the strings used in [`DecimalSymbolsV2`], i.e. a builder type
+/// for [`DecimalSymbolsStrs`]. This type can be obtained from a [`DecimalSymbolsStrs`]
+/// the `From`/`Into` traits.
 ///
 /// <div class="stab unstable">
 /// 🚧 This code is considered unstable; it may change at any time, in breaking or non-breaking ways,
@@ -116,6 +118,19 @@ pub struct DecimalSymbolStrsBuilder<'data> {
     pub grouping_separator: Cow<'data, str>,
 }
 
+impl<'data> DecimalSymbolStrsBuilder<'data> {
+    /// Build a [`DecimalSymbolsStrs`]
+    pub fn build(&self) -> VarZeroCow<'static, DecimalSymbolsStrs> {
+        VarZeroCow::from_encodeable(self)
+    }
+}
+
+impl<'data> From<&'data DecimalSymbolsStrs> for DecimalSymbolStrsBuilder<'data> {
+    fn from(other: &'data DecimalSymbolsStrs) -> Self {
+        zerofrom::ZeroFrom::zero_from(other)
+    }
+}
+
 /// Symbols and metadata required for formatting a [`FixedDecimal`](crate::FixedDecimal).
 ///
 /// <div class="stab unstable">

provider/source/src/decimal/mod.rs

@@ -122,7 +122,7 @@ impl SourceDataProvider {
     }
 
     /// Produce DataIdentifier's for all digit-based numbering systems in the form und/<numsys>
-    #[allow(unused)] // TODO configurable
+    #[allow(unused)] // TODO we should support using this, https://github.com/unicode-org/icu4x/issues/5824
     fn iter_all_number_ids(&self) -> Result<HashSet<DataIdentifierCow<'static>>, DataError> {
         use cldr_serde::numbering_systems::NumberingSystemType;
         let resource: &cldr_serde::numbering_systems::Resource = self

provider/source/src/decimal/symbols.rs

@@ -10,7 +10,6 @@ use icu_provider::prelude::*;
 use std::borrow::Cow;
 use std::collections::HashSet;
 use std::convert::TryFrom;
-use zerovec::VarZeroCow;
 
 impl DataProvider<DecimalSymbolsV2Marker> for SourceDataProvider {
     fn load(&self, req: DataRequest) -> Result<DataResponse<DecimalSymbolsV2Marker>, DataError> {
@@ -90,7 +89,7 @@ impl TryFrom<NumbersWithNumsys<'_>> for DecimalSymbolsV2<'static> {
             .map_err(|_| format!("Numbering system {nsname} should not be more than 8 bytes!"))?;
 
         Ok(Self {
-            strings: VarZeroCow::from_encodeable(&strings),
+            strings: strings.build(),
             grouping_sizes: GroupingSizesV1 {
                 primary: parsed_pattern.positive.primary_grouping,
                 secondary: parsed_pattern.positive.secondary_grouping,

tutorials/data_provider.md

@@ -196,7 +196,7 @@ The following example illustrates how to overwrite the decimal separators for a
 ```rust
 use core::any::Any;
 use icu::decimal::FixedDecimalFormatter;
-use icu::decimal::provider::DecimalSymbolsV2Marker;
+use icu::decimal::provider::{DecimalSymbolsV2Marker, DecimalSymbolStrsBuilder};
 use icu_provider::prelude::*;
 use icu_provider_adapters::fixed::FixedProvider;
 use icu::locale::locale;
@@ -217,8 +217,10 @@ where
         if req.id.locale.region == Some(region!("CH")) {
             if let Ok(mut decimal_payload) = res.payload.dynamic_cast_mut::<DecimalSymbolsV2Marker>() {
                 decimal_payload.with_mut(|data| {
-                    // Change the digit 0 for all Swiss locales to '🐮'
-                    data.digits[0] = '🐮';
+                    let mut builder = DecimalSymbolStrsBuilder::from(&*data.strings);
+                    // Change grouping separator for all Swiss locales to '🐮'
+                    builder.grouping_separator = "🐮".into();
+                    data.strings = builder.build();
                 });
             }
         }
@@ -249,7 +251,7 @@ let formatter = FixedDecimalFormatter::try_new_unstable(
 )
 .unwrap();
 
-assert_eq!(formatter.format_to_string(&100007i64.into()), "1🐮🐮,🐮🐮7");
+assert_eq!(formatter.format_to_string(&100007i64.into()), "100🐮007");
 ```
 
 ## Forking Data Providers