How does map correlate to AggregateFunction

[vinay2897]

This is a code snippet from uptrace here

type Measure struct {
        ....
	Histogram map[bfloat16.T]uint64 `ch:"type:AggregateFunction(quantilesBFloat16(0.5), Float32)"`
	...
}

quantilesBFloat16 accepts a Column with numeric data as input.

I am unable to understand how a map is being stored in quantilesBFloat16.