minted_geography

Coordinates and geohashes as well-modelled value types.

Part of the minted family: pure-Dart value types built on parse, don't validate, so the parser is the only door in and anything that came through it is well-formed by construction. Once you hold a GeoCoordinate, both halves are in range and in the order you meant; once you hold a Geohash, it decodes.

Install

dart pub add minted_geography

minted comes with it, holding the shared vocabulary (ParseOutcome, MintedFailure, Digit, Digits, the Uint tower). Nothing here drags in another domain's engine.

What's in the box

A swapped latitude and longitude is a type bug no range check catches, so the pair is named at the boundary. It's a surface coordinate: altitude and a CRS identifier are refused rather than silently dropped, since their sign, units and datum are all defined by the CRS.

A geohash is a cell, not a point, which a String cannot say: centre is one point inside it and says so. toLowerCase() isn't validation either, the alphabet having dropped a, i, l and o.

A quick taste

final eiffel = GeoCoordinate.tryParse('+48.8577+002.295/')!;
eiffel.latitude;     // 48.8577
eiffel.iso6709;      // '+48.8577+002.295/'   (canonical form)
eiffel.sexagesimal;  // '48°51′27.72″N 2°17′42″E'   (display form)

// ISO 6709 selects the unit by field width, and all three widths fold to degrees, so the same
// point spelled as degrees-minutes-seconds is the same value:
GeoCoordinate.tryParse('+485127.72+0021742/') == eiffel;   // true
GeoCoordinate.tryParse('+5012-00010/')!.latitude;          // 50.2   (degrees and minutes)

GeoCoordinate.tryParse('+46+2/');   // null: an unpadded longitude is a different location

// named, so it can't be written swapped:
GeoCoordinate.from(latitude: 48.8577, longitude: 2.295);

// Geohash: from takes a coordinate and cannot fail, so it hands back the value, not an outcome.
final cell = Geohash.from(coordinate: eiffel, precision: NaturalNumber.tryFrom(5)!);
cell.value;            // 'u09tu'   (canonical form: trimmed, lower-cased)
cell.centre.iso6709;   // '+48.84521484375+002.30712890625/'   inside the cell, not the tower

Geohash.tryParse('EZS42 ') == Geohash.tryParse('ezs42');   // true: case and padding fold away
Geohash.tryParse('ezsa2');   // null: 'a' is not in the geohash alphabet
['ezs42', 'ezs41', 'u4pruy']..sort();   // spatial order free: the alphabet is ASCII-ascending

The runnable version is the example.

One shape, every type

• GeoCoordinate.tryParse(input) hands back the value, or null when the input isn't valid
• GeoCoordinate.parse(input) hands back a ParseOutcome: the value, or a typed GeoCoordinateFailure you can switch on, or read as a form-field message via .reasonOrNull. No door throws
• value equality, a canonical form normalised on parse (.iso6709, Geohash.value), and from for parts you already hold, which for Geohash returns the value rather than an outcome

The minted README is the family guide: the whole catalogue, handling failures, and the one caveat (never cast into a minted type).