Many NSPredicate and NSExpression operators have no equivalent in style JSON

[1ec5]

This issue tracks progress toward supporting the full range of NSPredicate and NSExpression functions and operators, based on where we are in iOS map SDK v4.0.0 and macOS map SDK v0.7.0. mapbox/mapbox-gl-js#6484 is a corresponding issue that tracks several style specification additions that would block this goal.

Some of these operators already have workarounds. It isn’t necessary to support all of these operators, since some may be a poor fit for manipulating a style. Developers are used to – if sometimes frustrated by – the fact that various Core Data and NSArray backends support different subsets of the NSPredicate and NSExpression vocabulary and grammar.

• Types
  • NSSet
  • NSDate
  • CLLocation
• Basic comparisons
  • BETWEEN (worked around in v4.0.0/v0.7.0)
• String comparisons
  • BEGINSWITH (workaround would be possible with index-of: Add slice and index-of expressions mapbox-gl-js#9450)
  • CONTAINS: Remove “in” expression workaround mapbox-gl-native-ios#183
  • ENDSWITH (workaround would be possible with index-of: Add slice and index-of expressions mapbox-gl-js#9450)
  • LIKE
  • MATCHES: Implement "regex" expression that returns an array of match groups or… mapbox-gl-js#6228
  • UTI-CONFORMS-TO (probably not needed)
  • UTI-EQUALS (probably not needed)
• Aggregate expressions: Allow expressions as elements in array output values mapbox-gl-js#6155
• Aggregate operations
  • ANY, SOME: limited workaround in Remove “in” expression workaround mapbox-gl-native-ios#183
  • ALL: limited workaround in Remove “in” expression workaround mapbox-gl-native-ios#183
  • NONE: limited workaround in Remove “in” expression workaround mapbox-gl-native-ios#183
  • IN (MATCH is sort of a workaround): Remove “in” expression workaround mapbox-gl-native-ios#183
  • array[index] (needs a port of slice: Add slice and index-of expressions mapbox-gl-js#9450)
  • array[FIRST]: [ios, macos] Add support for subscripting in expressions. #11770
  • array[LAST]: [ios, macos] Add support for subscripting in expressions. #11770
  • array[SIZE]: [ios, macos] Add support for subscripting in expressions. #11770
• SUBQUERY (like a list comprehension)
• Set operations
  • UNION (not supported by Core Data)
  • INTERSECT (not supported by Core Data)
  • MINUS (not supported by Core Data)
• Operator modifiers
  • c for case insensitivity: Port 'Collator' string comparison support to native #11692 Convert between predicate options and collator expressions #12329
  • d for diacritic insensitivity: Case and diacritic folding for expression operators mapbox-gl-js#4136 Convert between predicate options and collator expressions #12329
  • l for locale insensitivity: Port 'Collator' string comparison support to native #11692 [ios, macos] Write "collator" wrappers for NSExpression #12269
  • n for normalization
• Functions
  • average: (worked around in v4.0.0/v0.7.0)
  • median:: Add some missing math expressions mapbox-gl-js#5853
  • mode:: Add some missing math expressions mapbox-gl-js#5853
  • stddev:: Add some missing math expressions mapbox-gl-js#5853
  • exp: (worked around in v4.0.0/v0.7.0): Add some missing math expressions mapbox-gl-js#5853
  • trunc: (worked around in v4.0.0/v0.7.0)
  • random: Add some missing math expressions mapbox-gl-js#5853
  • randomn:: Add some missing math expressions mapbox-gl-js#5853
  • now
  • bitwiseAnd:with:
  • bitwiseOr:with:
  • bitwiseXor:with:
  • leftshift:by:
  • rightshift:by:
  • onesComplement:
  • distanceToLocation:fromLocation:: Add distance expression function mapbox-gl-native-ios#295 gets us pretty close
• Collection operators
  • array.subkey (mapping an array to a subkey of its elements)
  • @avg
  • @count
  • @min
  • @max
  • @sum
  • @distinctUnionOfObjects
  • @unionOfObjects
  • @distinctUnionOfArrays
  • @unionOfArrays
  • @distinctUnionOfSets
• Casts – technically, any Objective-C object can be cast to an NSString, but the items below are for expected use cases
  • NSArray → NSString
  • NSDictionary → NSString
  • NSDate → NSString
  • NSColor/UIColor → NSString
  • NSArray → NSString
  • NSString → NSDate
  • NSNumber → NSDate
• Block expressions – blocked by Data-driven styling should support arbitrary functions #7860

(Sources for this issue included Realm’s “NSPredicate Cheatsheet”.)

/ref mapbox/mapbox-gl-js#5892
/cc @fabian-guerra @anandthakker @ChrisLoer

[stale]

This issue has been automatically detected as stale because it has not had recent activity and will be archived. Thank you for your contributions.

[1ec5]

I added a note that block expressions are, ahem, blocked by core support as described in #7860. If there’s any way at all that we could support arbitrary executable code as part of style property evaluation, we should definitely consider it, because developers find it much more straightforward to use ordinary programming language affordances than to learn a declarative mini-language, be it NSExpression format strings or anything we’d implement in the style spec for Turing completeness.

[stale]

This issue has been automatically detected as stale because it has not had recent activity and will be archived. Thank you for your contributions.