Expression: "The dentist told me that I'll have to..."

[Tom]

Hi

Yesterday I read a sentence in Oxford Idioms which confused me a bit. Can we use I'll with the past tense without speech marks?

Quote:

The dentist told me I'll have to have this tooth out.

Please shed some light on this.

Tom

[Alan]

Hi Tom,

Probably the purist in you wants to say: 'I'd have to ...', which would follow the usual pattern. But by using 'I'll have to ..' the statement becomes more immediate and relates more closely back to what the dentist actually said. Does that help at all?

Alan
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[Tom]

I am grateful, Alan

So am I to understand that past tense+ will is not a grammatical mistake at all? Can I use this form frequently? For example:

[Tom]

Hello

Anyone there?

Tom

[Yankee]