Add new builtin for merging maps
Author: dnbsdCreated Dec 31, 2025Updated Mar 19, 2026
Labelsfeature
Expr currently does not have a builtin for merging maps. Adding a new builtin would be useful to merge maps but also to modify nested fields.
For instance:
/*
Env:
{
"data":{
"status": 0,
"rows": 32,
"signing_keys":[
"key1",
"key2"
]
}
}
*/
merge($env["data"], {signing_keys: concat($env["data"]["signing_keys"], ["another"])})
/*
Output:
{
"data":{
"status": 0,
"rows": 32,
"signing_keys":[
"key1",
"key2",
"another"
]
}
}
*/As for the name, "merge" seems natural but I would also consider using "copy" (as used in Go's maps package). Other possibility is to modify "concat" to support both arrays and maps.
Source: expr-lang/expr