173 lines
4.1 KiB
Markdown
173 lines
4.1 KiB
Markdown
# Dictionaries and Dict Functions
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Sprig provides a key/value storage type called a `dict` (short for "dictionary",
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as in Python). A `dict` is an _unorder_ type.
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The key to a dictionary **must be a string**. However, the value can be any
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type, even another `dict` or `list`.
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Unlike `list`s, `dict`s are not immutable. The `set` and `unset` functions will
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modify the contents of a dictionary.
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## dict
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Creating dictionaries is done by calling the `dict` function and passing it a
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list of pairs.
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The following creates a dictionary with three items:
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```
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$myDict := dict "name1" "value1" "name2" "value2" "name3" "value 3"
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```
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## get
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Given a map and a key, get the value from the map.
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```
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get $myDict "name1"
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```
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The above returns `"value1"`
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Note that if the key is not found, this operation will simply return `""`. No error
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will be generated.
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## set
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Use `set` to add a new key/value pair to a dictionary.
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```
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$_ := set $myDict "name4" "value4"
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```
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Note that `set` _returns the dictionary_ (a requirement of Go template functions),
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so you may need to trap the value as done above with the `$_` assignment.
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## unset
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Given a map and a key, delete the key from the map.
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```
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$_ := unset $myDict "name4"
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```
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As with `set`, this returns the dictionary.
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Note that if the key is not found, this operation will simply return. No error
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will be generated.
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## hasKey
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The `hasKey` function returns `true` if the given dict contains the given key.
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```
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hasKey $myDict "name1"
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```
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If the key is not found, this returns `false`.
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## pluck
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The `pluck` function makes it possible to give one key and multiple maps, and
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get a list of all of the matches:
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```
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pluck "name1" $myDict $myOtherDict
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```
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The above will return a `list` containing every found value (`[value1 otherValue1]`).
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If the give key is _not found_ in a map, that map will not have an item in the
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list (and the length of the returned list will be less than the number of dicts
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in the call to `pluck`.
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If the key is _found_ but the value is an empty value, that value will be
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inserted.
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A common idiom in Sprig templates is to uses `pluck... | first` to get the first
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matching key out of a collection of dictionaries.
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## dig
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The `dig` function traverses a nested set of dicts, selecting keys from a list
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of values. It returns a default value if any of the keys are not found at the
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associated dict.
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```
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dig "user" "role" "humanName" "guest" $dict
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```
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Given a dict structured like
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```
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{
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user: {
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role: {
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humanName: "curator"
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}
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}
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}
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```
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the above would return `"curator"`. If the dict lacked even a `user` field,
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the result would be `"guest"`.
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Dig can be very useful in cases where you'd like to avoid guard clauses,
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especially since Go's template package's `and` doesn't shortcut. For instance
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`and a.maybeNil a.maybeNil.iNeedThis` will always evaluate
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`a.maybeNil.iNeedThis`, and panic if `a` lacks a `maybeNil` field.)
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`dig` accepts its dict argument last in order to support pipelining.
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## keys
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The `keys` function will return a `list` of all of the keys in one or more `dict`
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types. Since a dictionary is _unordered_, the keys will not be in a predictable order.
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They can be sorted with `sortAlpha`.
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```
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keys $myDict | sortAlpha
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```
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When supplying multiple dictionaries, the keys will be concatenated. Use the `uniq`
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function along with `sortAlpha` to get a unqiue, sorted list of keys.
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```
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keys $myDict $myOtherDict | uniq | sortAlpha
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```
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## pick
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The `pick` function selects just the given keys out of a dictionary, creating a
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new `dict`.
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```
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$new := pick $myDict "name1" "name2"
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```
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The above returns `{name1: value1, name2: value2}`
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## omit
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The `omit` function is similar to `pick`, except it returns a new `dict` with all
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the keys that _do not_ match the given keys.
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```
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$new := omit $myDict "name1" "name3"
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```
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The above returns `{name2: value2}`
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## values
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The `values` function is similar to `keys`, except it returns a new `list` with
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all the values of the source `dict` (only one dictionary is supported).
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```
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$vals := values $myDict
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```
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The above returns `list["value1", "value2", "value 3"]`. Note that the `values`
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function gives no guarantees about the result ordering- if you care about this,
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then use `sortAlpha`.
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