Add expression operator testing whether a string contains a substring

[lucaswoj]

From @vicapow on April 5, 2016 22:46

This would be useful for showing query results as the user types.

Copied from original issue: mapbox/mapbox-gl-style-spec#438

[lucaswoj]

Closely related to #233

[1ec5]

Now that expressions have landed and can be used as filters, this is actually a request to add an expression operator. Specifically, there should be an operator that tests whether a string contains another string.

By analogy, the most likely syntax would be ["match", needleString, haystackString]. However, the word “match” is more closely associated with wildcards and regular expressions, which are covered by #4089. As I mentioned in #5226 (comment), in Objective-C and Swift, NSPredicate has a CONTAINS operator that serves as both an array search operator and a substring search operator (#4113), depending on the type of the first argument. It’s a convenient option even when a MATCHES operator exists for regular expressions.

[arethasamuel]

Hi When will this feature be ready? autocomplete search is one of our main use cases, is there an alternative way of doing a "contains" search?

[andrewharvey]

@arethasamuel if your data isn't too big you could keep an external list of the query properties from your features and filter based on the full list of names which match the user input.

[anandthakker]

@arethasamuel the best place to track this at the moment is via the discussion about regexp expressions happening at #6228. As you can see from that conversation, we're still hashing out the right API design, so there's no concrete timeline for when this functionality will be available.

[pshavr]

so
when substr?)

[dwohlfahrt]

I'll second @pshavr 's request for a substring function and associated expression syntax!

[1ec5]

A substring test expression would make it easy to implement these road maps color-coded by street name suffix in GL.

[ryanhamley]

A substring test expression would make it easy to implement these road maps color-coded by street name suffix in GL.

Here's an example of the color-coded road maps mentioned by @1ec5
https://jsfiddle.net/rsh412/Ldn39w0x/4/