How to dynamically adjust the symbol input for request.security in Pinescript based off a string?

Question

I want to select the Futures Contract of CL, based on the month and year we're in, so that it dynamically adjusts over time. This is what I tried:

//@version=5
indicator("CL-Futures", shorttitle="FL", overlay=false)

string CL = "CL"

string oct23 = "V2023"
string nov23 = "X2023"
string dez23 = "Z2023"

var string m1 = na

if month(time) == 10 and year(time) == 2023 
    m1 := oct23
if month(time) == 11 and year(time) == 2023 
    m1 := nov23
if month(time) == 12 and year(time) == 2023 
    m1 := dez23

f1  =  request.security(CL + m1  , "", close)


// I get the following error message at the request.security function 

Cannot call 'request.security' with argument 'symbol'='call 'operator +' (series string)'. An argument of 'series string' type was used but a 'simple string' is expected.

Does anybody know a fix?

Answer 1

I didn't quite understand what you want to show on the chart.

If the month and year matches then plot the month's contract? If that's what you're asking, this is one way to plot. Remember that the October contract has expired.

//@version=5
indicator("CL-Futures", shorttitle="FL", overlay=false)

bool x1_bool = false
bool x2_bool = false
bool x3_bool = false

if month(time) == 10 and year(time) == 2023 
    x1_bool := true
if month(time) == 11 and year(time) == 2023 
    x2_bool := true
if month(time) == 12 and year(time) == 2023 
    x3_bool := true

x1 = request.security('NYMEX:CLV2023', "", close) // Expired Contract
x2 = request.security('NYMEX:CLX2023', "", close)
x3 = request.security('NYMEX:CLZ2023', "", close)


plot(x1_bool ? x1: na, title='October  2023', color=color.green)
plot(x2_bool ? x2: na, title='November 2023', color=color.red)
plot(x3_bool ? x3: na, title='December 2023', color=color.blue)

However, you get an error because you are passing a serial string instead of a simple string. it means that the value of the string you are trying to pass through cannot change during script runtime.

To work correctly it needs a simple fixed string that works as if it were a constant. This is why you get that error