NewDerive initializes a new Derive, registers it with the "expvar" package and returns it.

NewDeriveString parses s as an Identifier and returns a new Derive.

NewGauge initializes a new Gauge, registers it with the "expvar" package and returns it.

NewGaugeString parses s as an Identifier and returns a new Gauge.

Publish adds v to the internal list of exported metrics.

Run periodically calls the ValueList function of each Var, sets the Time and Interval fields and passes it w.Write().

Derive represents a cumulative integer data type, for example "requests served since server start".

Gauge represents an absolute floating point data type, for example "heap memory used".

Options holds options for the Run() function.

Var is an abstract type for metrics exported by this package.