cannot range over
Go Compiler Error
Severity: MinorWhat Does This Error Mean?
The Go 'cannot range over' error means you are using a range loop on a type that is not rangeable. Range works on arrays, slices, maps, strings, and channels. You cannot range over an integer, struct, or interface without type-asserting it first.
Affected Models
- Go 1.x (all versions)
Common Causes
- Using range on an integer variable instead of a slice
- Ranging over a nil pointer or unexported interface
- Using range on a struct that should be a slice of structs
- Variable declared as interface{} holding a slice — must be type-asserted first
- Attempting to range over a custom type with a non-rangeable underlying type
How to Fix It
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Check the type of the variable you are ranging over.
The error message includes the type. If it says cannot range over x (type int), x is a number, not a slice. Ensure the variable holds a slice, array, map, string, or channel.
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If ranging over an interface{} or any, type-assert it first.
Example: if items, ok := data.([]string); ok { for _, item := range items { ... } } An interface value must be asserted to its concrete slice type before ranging.
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To loop N times without a slice, use a traditional for loop.
In Go 1.22+, you can write: for i := range 10 {} In earlier versions, use: for i := 0; i < n; i++ {} to loop a fixed number of times.
Frequently Asked Questions
Can you range over a map in Go?
Yes — ranging over a map gives key and value pairs on each iteration: for k, v := range myMap {} Note that map iteration order is randomised in Go — never assume a specific order.
Can you range over a channel in Go?
Yes — ranging over a channel reads values until the channel is closed: for v := range ch {} The loop exits when the channel is closed. If the channel is never closed, the loop blocks indefinitely.