For example, in badly inferred code, one may obtain
julia> @code_warntype (x -> convert(Int, x[1]))(Any[1])
MethodInstance for (::var"#3#4")(::Vector{Any})
from (::var"#3#4")(x) @ Main REPL[5]:1
Arguments
#self#::Core.Const(var"#3#4"())
x::Vector{Any}
Body::Any
1 ─ %1 = Base.getindex(x, 1)::Any
│ %2 = Main.convert(Main.Int, %1)::Any
└── return %2
However, the only sensible type that should be returned here is Int. With a type-assertion, we would obtain
julia> _convert(::Type{T}, x::T) where {T} = convert(T, x)::T
_convert (generic function with 1 method)
julia> @code_warntype (x -> _convert(Int, x[1]))(Any[1])
MethodInstance for (::var"#5#6")(::Vector{Any})
from (::var"#5#6")(x) @ Main REPL[8]:1
Arguments
#self#::Core.Const(var"#5#6"())
x::Vector{Any}
Body::Int64
1 ─ %1 = Base.getindex(x, 1)::Any
│ %2 = Main._convert(Main.Int, %1)::Int64
└── return %2