github.com/cockroachdb/cockroach@v20.2.0-alpha.1+incompatible/pkg/sql/sem/tree/aggregate_funcs.go (about)

     1  // Copyright 2017 The Cockroach Authors.
     2  //
     3  // Use of this software is governed by the Business Source License
     4  // included in the file licenses/BSL.txt.
     5  //
     6  // As of the Change Date specified in that file, in accordance with
     7  // the Business Source License, use of this software will be governed
     8  // by the Apache License, Version 2.0, included in the file
     9  // licenses/APL.txt.
    10  
    11  package tree
    12  
    13  import "context"
    14  
    15  // AggregateFunc accumulates the result of a function of a Datum.
    16  type AggregateFunc interface {
    17  	// Add accumulates the passed datums into the AggregateFunc.
    18  	// Most implementations require one and only one firstArg argument.
    19  	// If an aggregate function requires more than one argument,
    20  	// all additional arguments (after firstArg) are passed in as a
    21  	// variadic collection, otherArgs.
    22  	// This interface (as opposed to `args ...Datum`) avoids unnecessary
    23  	// allocation of otherArgs in the majority of cases.
    24  	Add(_ context.Context, firstArg Datum, otherArgs ...Datum) error
    25  
    26  	// Result returns the current value of the accumulation. This value
    27  	// will be a deep copy of any AggregateFunc internal state, so that
    28  	// it will not be mutated by additional calls to Add.
    29  	Result() (Datum, error)
    30  
    31  	// Reset resets the aggregate function which allows for reusing the same
    32  	// instance for computation without the need to create a new instance.
    33  	// Any memory is kept, if possible.
    34  	Reset(context.Context)
    35  
    36  	// Close closes out the AggregateFunc and allows it to release any memory it
    37  	// requested during aggregation, and must be called upon completion of the
    38  	// aggregation.
    39  	Close(context.Context)
    40  
    41  	// Size returns the size of the AggregateFunc implementation in bytes. It
    42  	// does *not* account for additional memory used during accumulation.
    43  	Size() int64
    44  }