message: use concrete return type, fixes
diff: @@ -8,7 +8,6 @@ use crate::space_usage::PerFieldSpaceUsage;
  use crate::TantivyError;
  use super::reader::DynamicFastFieldReader;
  -use super::FastFieldReader;
  /// Provides access to all of the BitpackedFastFieldReader.
  ///
  @@ -138,7 +137,7 @@ impl FastFieldReaders {
  /// Returns the `i64` fast field reader reader associated to `field`.
  ///
  /// If `field` is not a i64 fast field, this method returns an Error.
  - pub fn i64(&self, field: Field) -> crate::Result<impl FastFieldReader<i64>> {
  + pub fn i64(&self, field: Field) -> crate::Result<DynamicFastFieldReader<i64>> {
  self.check_type(field, FastType::I64, Cardinality::SingleValue)?;
  self.typed_fast_field_reader(field)
  }
  @@ -146,7 +145,7 @@ impl FastFieldReaders {
  /// Returns the `i64` fast field reader reader associated to `field`.
  ///
  /// If `field` is not a i64 fast field, this method returns an Error.
  - pub fn date(&self, field: Field) -> crate::Result<impl FastFieldReader<crate::DateTime>> {
  + pub fn date(&self, field: Field) -> crate::Result<DynamicFastFieldReader<crate::DateTime>> {
  self.check_type(field, FastType::Date, Cardinality::SingleValue)?;
  self.typed_fast_field_reader(field)
  }
  @@ -154,7 +153,7 @@ impl FastFieldReaders {
  /// Returns the `f64` fast field reader reader associated to `field`.
  ///
  /// If `field` is not a f64 fast field, this method returns an Error.
  - pub fn f64(&self, field: Field) -> crate::Result<impl FastFieldReader<f64>> {
  + pub fn f64(&self, field: Field) -> crate::Result<DynamicFastFieldReader<f64>> {
  self.check_type(field, FastType::F64, Cardinality::SingleValue)?;
  self.typed_fast_field_reader(field)
  }
  