Data Types 2

When you first started this course, you learned about primitive data types. In the previous chapter we name-dropped two more types: “slice”, and “sdict” (“map”), both without much elaboration. In this chapter, we will explore these data types in more detail.

Slices#

A slice is an ordered list of items. In custom commands, we can create a slice by providing the items in order to the cslice function:

{{ $fruits := cslice "banana" "orange" "apple" }}

All the elements in the $fruits slice happen to have the same type (string), but this is not a requirement: it is valid, though rare, for a slice to contain elements of different types.

Besides primitives, slices may also contain more complex data types. In previous chapters, for instance, we represented the fields of an embed as a slice of dictionaries.

For available operations on slices, please refer to our template documentation.

{{ $users := cslice }} {{/* imagine this data is dynamically generated */}}
{{ if $users }}
    one or more users
{{ else }}
    no users
{{ end }}

Maps#

A map is a table that associates values with keys, such that it is easy and efficient to retrieve the value corresponding to a given key.

For example, a program that implements a reputation system might wish to use a map from user IDs (key) to reputation points (value) internally. Using this map, the program can quickly look up and modify the reputation points for any given user.

Custom commands offer two kinds of maps: sdicts and dicts. A sdict only supports string keys (hence the name: string dictionary), whereas a dict supports all comparable data types.

To create a map, provide a sequence of key-value pairs to the sdict or the dict function as appropriate:

{{ $fruitPrices := sdict "pineapple" 3.50 "apple" 1.50 "banana" 2.60 }}

{{/* For readability, it's common to put each key/value pair on a new line. */}}
{{ $userReputation := dict
    935212563644420158 3
    204255221017214977 5
}}

{{/* Pass no arguments for an empty map. */}}
{{ $empty := sdict }}

As with slices, empty maps are falsy and so can be used directly in conditional statements.

For available operations on maps, please refer to our template documentation.

{{ $fruitPrices := sdict "pineapple" 3.50 "apple" 1.50 "banana" 2.60 }}
{{ $fruitPrices }}

map[apple:1.5 banana:2.6 pineapple:3.5]