You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: constant.rs
    path of file: ./repos/surrealdb/core/src/sql/v2
    
    the code of the file until where you have to start completion: use crate::ctx::Context;
use crate::dbs::{Options, Transaction};
use crate::doc::CursorDoc;
use crate::err::Error;
use crate::sql::value::Value;
use crate::sql::Datetime;
use chrono::TimeZone;
use chrono::Utc;
use derive::Store;
use revision::revisioned;
use serde::{Deserialize, Serialize};
use std::fmt;

pub(crate) const TOKEN: &str = "$surrealdb::private::sql::Constant";

#[derive(Clone, Debug, Eq, PartialEq, PartialOrd, Serialize, Deserialize, Store, Hash)]
#[serde(rename = "$surrealdb::private::sql::Constant")]
#[revisioned(revision = 1)]
#[cfg_attr(feature = "arbitrary", derive(arbitrary::Arbitrary))]
pub enum Constant {
	MathE,
	MathFrac1Pi,
	MathFrac1Sqrt2,
	MathFrac2Pi,
	MathFrac2SqrtPi,
	MathFracPi2,
	MathFracPi3,
	MathFracPi4,
	MathFracPi6,
	MathFracPi8,
	MathInf,
	MathLn10,
	MathLn2,
	MathLog102,
	MathLog10E,
	MathLog210,
	MathLog2E,
	MathPi,
	MathSqrt2,
	MathTau,
	TimeEpoch,
	// Add new variants here
}

/// A type of constant that may be converted to a value or JSON.
pub(crate) enum ConstantValue {
	Float(f64),
	Datetime(Datetime),
}

impl Const
    
	pub(crate) fn value(&self) -> ConstantValue {
		use std::f64::consts as f64c;
		match self {
			Self::MathE => ConstantValue::Float(f64c::E),
			Self::MathFrac1Pi => ConstantValue::Float(f64c::FRAC_1_PI),
			Self::MathFrac1Sqrt2 => ConstantValue::Float(f64c::FRAC_1_SQRT_2),
			Self::MathFrac2Pi => ConstantValue::Float(f64c::FRAC_2_PI),
			Self::MathFrac2SqrtPi => ConstantValue::Float(f64c::FRAC_2_SQRT_PI),
			Self::MathFracPi2 => ConstantValue::Float(f64c::FRAC_PI_2),
			Self::MathFracPi3 => ConstantValue::Float(f64c::FRAC_PI_3),
			Self::MathFracPi4 => ConstantValue::Float(f64c::FRAC_PI_4),
			Self::MathFracPi6 => ConstantValue::Float(f64c::FRAC_PI_6),
			Self::MathFracPi8 => ConstantValue::Float(f64c::FRAC_PI_8),
			Self::MathInf => ConstantValue::Float(f64::INFINITY),
			Self::MathLn10 => ConstantValue::Float(f64c::LN_10),
			Self::MathLn2 => ConstantValue::Float(f64c::LN_2),
			Self::MathLog102 => ConstantValue::Float(f64c::LOG10_2),
			Self::MathLog10E => ConstantValue::Float(f64c::LOG10_E),
			Self::MathLog210 => ConstantValue::Float(f64c::LOG2_10),
			Self::MathLog2E => ConstantValue::Float(f64c::LOG2_E),
			Self::MathPi => ConstantValue::Float(f64c::PI),
			Self::MathSqrt2 => ConstantValue::Float(f64c::SQRT_2),
			Self::MathTau => ConstantValue::Float(f64c::TAU),
			Self::TimeEpoch => ConstantValue::Datetime(Datetime(Utc.timestamp_nanos(0))),
		}
	}